Is there a clean (and null safe) way to multiply the values of a map in Java?

up vote
6
down vote

favorite

I have a Map<String, Double>, and want to multiply all the values in the map by 2, say, but keep the nulls as nulls.

I can obviously use a for loop to do this, but was wondering if there was a cleaner way to do so?

Map<String, Double> someMap = someMapFunction();
Map<String, Double> adjustedMap = new Hashmap<>();
if (someMap != null) 
 for (Map.Entry<String,Double> pair : someMap.entryset()) 
 if (pair.getValue() == null) 
 adjustedMap.put(pair.getKey(), pair.getValue());
 else 
 adjustedMap.put(pair.getKey(), pair.getValue()*2)

Also sometimes the map returned by someMapFunction is an immutable map, so this can't be done in place using Map.replaceAll. I couldn't come up with a stream solution that was cleaner

edited 27 mins ago

Michael

16.7k63066

asked 44 mins ago

Omar Haque

1335

add a commentÂ |Â

up vote
6
down vote

favorite

I have a Map<String, Double>, and want to multiply all the values in the map by 2, say, but keep the nulls as nulls.

I can obviously use a for loop to do this, but was wondering if there was a cleaner way to do so?

Map<String, Double> someMap = someMapFunction();
Map<String, Double> adjustedMap = new Hashmap<>();
if (someMap != null) 
 for (Map.Entry<String,Double> pair : someMap.entryset()) 
 if (pair.getValue() == null) 
 adjustedMap.put(pair.getKey(), pair.getValue());
 else 
 adjustedMap.put(pair.getKey(), pair.getValue()*2)

Also sometimes the map returned by someMapFunction is an immutable map, so this can't be done in place using Map.replaceAll. I couldn't come up with a stream solution that was cleaner

edited 27 mins ago

Michael

16.7k63066

asked 44 mins ago

Omar Haque

1335

add a commentÂ |Â

up vote
6
down vote

favorite

I have a Map<String, Double>, and want to multiply all the values in the map by 2, say, but keep the nulls as nulls.

I can obviously use a for loop to do this, but was wondering if there was a cleaner way to do so?

Map<String, Double> someMap = someMapFunction();
Map<String, Double> adjustedMap = new Hashmap<>();
if (someMap != null) 
 for (Map.Entry<String,Double> pair : someMap.entryset()) 
 if (pair.getValue() == null) 
 adjustedMap.put(pair.getKey(), pair.getValue());
 else 
 adjustedMap.put(pair.getKey(), pair.getValue()*2)

Also sometimes the map returned by someMapFunction is an immutable map, so this can't be done in place using Map.replaceAll. I couldn't come up with a stream solution that was cleaner

edited 27 mins ago

Michael

16.7k63066

asked 44 mins ago

Omar Haque

1335

I have a Map<String, Double>, and want to multiply all the values in the map by 2, say, but keep the nulls as nulls.

I can obviously use a for loop to do this, but was wondering if there was a cleaner way to do so?

Map<String, Double> someMap = someMapFunction();
Map<String, Double> adjustedMap = new Hashmap<>();
if (someMap != null) 
 for (Map.Entry<String,Double> pair : someMap.entryset()) 
 if (pair.getValue() == null) 
 adjustedMap.put(pair.getKey(), pair.getValue());
 else 
 adjustedMap.put(pair.getKey(), pair.getValue()*2)

Also sometimes the map returned by someMapFunction is an immutable map, so this can't be done in place using Map.replaceAll. I couldn't come up with a stream solution that was cleaner

java java-8 java-stream

edited 27 mins ago

Michael

16.7k63066

asked 44 mins ago

Omar Haque

1335

edited 27 mins ago

Michael

16.7k63066

asked 44 mins ago

Omar Haque

1335

edited 27 mins ago

Michael

16.7k63066

edited 27 mins ago

Michael

16.7k63066

edited 27 mins ago

Michael

16.7k63066

asked 44 mins ago

Omar Haque

1335

asked 44 mins ago

Omar Haque

1335

asked 44 mins ago

Omar Haque

1335

add a commentÂ |Â

8 Answers
8

active

oldest

votes

up vote
3
down vote

accepted

As an alternative to streaming and/or copying solutions, the Maps.transformValues() utility method exists in Google Guava:

Map<String, Double> adjustedMap = Maps.transformValues(someMap, value -> (value != null) ? (2 * value) : null);

This returns a lazy view of the original map that does not do any work on its own, but applies the given function when needed. This can be both a pro (if you're unlikely to ever need all the values, this will save you some computing time) and a con (if you'll need the same value many times, or if you need to further change someMap without adjustedMap seeing the changes) depending on your usage.

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

add a commentÂ |Â

up vote
8
down vote

You can create a copy of the original map and then call replaceAll:

Map<String, Double> adjustedMap = new HashMap<>(someMap);
adjustedMap.replaceAll ((k,v) -> v != null ? 2*v : null);

edited 25 mins ago

answered 36 mins ago

Eran

267k34409496

add a commentÂ |Â

up vote
2
down vote

It can be done like that

someMap.entrySet().stream()
 .filter(stringDoubleEntry -> stringDoubleEntry.getValue() != null) //filter null values out
 .forEach(stringDoubleEntry -> stringDoubleEntry.setValue(stringDoubleEntry.getValue() * 2)); //multiply values which are not null

In case you need a second map where just values in which are not null just use the forEach to put them into your new map.

answered 31 mins ago

CodeMatrix

8251519

1

This solution does what the OP's code does in a nice form (though stringDoubleEntry is a bit unaccustomedly long). It exploits that the entries are backed by the map; no new map is created.
â€“Â Joop Eggen
17 mins ago

1

I did not want to criticize, indeed the other way around. There was no upvote and others were already upvoted, despite your solution being straight-forward efficient.
â€“Â Joop Eggen
12 mins ago

My mistake I read over 2 words which were the key that was different haha.
â€“Â CodeMatrix
10 mins ago

add a commentÂ |Â

up vote
2
down vote

You can achieve that by converting into a stream, something like:

 someMap.entrySet()
 .forEach(entry -> 
 if(entry.getValue() != null) 
 adjustedMap.put(entry.getKey(), someMap.get(entry.getKey()) * 2);
 else 
 adjustedMap.put(entry.getKey(), null);
 
 );

which can be shorted to :

someMap.forEach((key, value) -> 
 if (value != null) 
 adjustedMap.put(key, value * 2);
 else 
 adjustedMap.put(key, null);
 
 );

So, if you'r having a map with:

Map<String, Double> someMap = new HashMap<>();
someMap.put("test1", 1d);
someMap.put("test2", 2d);
someMap.put("test3", 3d);
someMap.put("testNull", null);
someMap.put("test4", 4d);

You will get this output:

test4=8.0, test2=4.0, test3=6.0, testNull=null, test1=2.0

edited 2 mins ago

answered 34 mins ago

Leviand

1,3881122

3

The OP wanted to "keep the nulls as nulls.", not filter them out.
â€“Â Eran
22 mins ago

@Eran My bad, i'm fixing, thanks
â€“Â Leviand
21 mins ago

@Eran fixed, thanks for pointing it
â€“Â Leviand
9 mins ago

Your someMap.get(key) can be simply value instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
3 mins ago

add a commentÂ |Â

up vote
1
down vote

Use like this.

 Map<String, Double> adjustedMap = map.entrySet().stream()filter(x -> x.getValue() != null)
 .collect(Collectors.toMap(x -> x.getKey(), x -> 2*x.getValue()));
 //printing 
 adjustedMap.entrySet().stream().forEach(System.out::println);

edited 23 mins ago

answered 30 mins ago

amitpandey

158111

This is not null safe
â€“Â Eran
26 mins ago

add a commentÂ |Â

up vote
1
down vote

You can do this with this code:

 Map<String, Double> map = new HashMap<>();
 map.put("1", 3.0);
 map.put("3", null);
 map.put("2", 5.0);

 Map<String, Double> res = map.entrySet().stream()
 .collect(HashMap::new, (m,v)->m.put(v.getKey(), v.getValue() != null ? v.getValue() * 2 : null), HashMap::putAll);

 System.out.println(res);

and the output will be:

1=6.0, 2=10.0, 3=null

It will allow you to keep null values in the map.

edited 18 mins ago

answered 24 mins ago

user987339

7,86862936

add a commentÂ |Â

up vote
1
down vote

To keep null values you can use something as simple as :

someMap.keySet()
 .stream()
 .forEach(key -> adjustedMap.put(key, (someMap.get(key)) == null ? null : someMap.get(key) * 2));

answered 18 mins ago

c0der

7,31241643

You should absolutely stream on the entrySet(), they you'd avoid calling someMap.get(key) in a loop, and would be able to just do entry.value() instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
5 mins ago

add a commentÂ |Â

up vote
1
down vote

Try something like this with java 8 steam api

Map<String, Double> newMap = oldMap.entrySet().stream()
 .collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue() == null ? null: x.getValue()*2));

edited 14 mins ago

Nicholas K

2,6502725

answered 27 mins ago

oguzhan aygun

3018

This will throw NullPointerException for any null values.
â€“Â Eran
24 mins ago

how is it possible ?
â€“Â oguzhan aygun
22 mins ago

3

That's the behavior of Collectors.toMap. You can try it and see for yourself.
â€“Â Eran
20 mins ago

thank you Eran I just tried and learn something new :)
â€“Â oguzhan aygun
14 mins ago

add a commentÂ |Â

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8 Answers
8

active

oldest

votes

8 Answers
8

active

oldest

votes

up vote
3
down vote

accepted

As an alternative to streaming and/or copying solutions, the Maps.transformValues() utility method exists in Google Guava:

Map<String, Double> adjustedMap = Maps.transformValues(someMap, value -> (value != null) ? (2 * value) : null);

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

add a commentÂ |Â

up vote
3
down vote

accepted

As an alternative to streaming and/or copying solutions, the Maps.transformValues() utility method exists in Google Guava:

Map<String, Double> adjustedMap = Maps.transformValues(someMap, value -> (value != null) ? (2 * value) : null);

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

add a commentÂ |Â

up vote
3
down vote

accepted

As an alternative to streaming and/or copying solutions, the Maps.transformValues() utility method exists in Google Guava:

Map<String, Double> adjustedMap = Maps.transformValues(someMap, value -> (value != null) ? (2 * value) : null);

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

As an alternative to streaming and/or copying solutions, the Maps.transformValues() utility method exists in Google Guava:

Map<String, Double> adjustedMap = Maps.transformValues(someMap, value -> (value != null) ? (2 * value) : null);

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

answered 14 mins ago

Petr JaneÃ„Âek

28.9k887122

add a commentÂ |Â

up vote
8
down vote

You can create a copy of the original map and then call replaceAll:

Map<String, Double> adjustedMap = new HashMap<>(someMap);
adjustedMap.replaceAll ((k,v) -> v != null ? 2*v : null);

edited 25 mins ago

answered 36 mins ago

Eran

267k34409496

add a commentÂ |Â

up vote
8
down vote

You can create a copy of the original map and then call replaceAll:

Map<String, Double> adjustedMap = new HashMap<>(someMap);
adjustedMap.replaceAll ((k,v) -> v != null ? 2*v : null);

edited 25 mins ago

answered 36 mins ago

Eran

267k34409496

add a commentÂ |Â

up vote
8
down vote

You can create a copy of the original map and then call replaceAll:

Map<String, Double> adjustedMap = new HashMap<>(someMap);
adjustedMap.replaceAll ((k,v) -> v != null ? 2*v : null);

edited 25 mins ago

answered 36 mins ago

Eran

267k34409496

You can create a copy of the original map and then call replaceAll:

Map<String, Double> adjustedMap = new HashMap<>(someMap);
adjustedMap.replaceAll ((k,v) -> v != null ? 2*v : null);

edited 25 mins ago

answered 36 mins ago

Eran

267k34409496

edited 25 mins ago

answered 36 mins ago

Eran

267k34409496

answered 36 mins ago

Eran

267k34409496

answered 36 mins ago

Eran

267k34409496

add a commentÂ |Â

up vote
2
down vote

It can be done like that

someMap.entrySet().stream()
 .filter(stringDoubleEntry -> stringDoubleEntry.getValue() != null) //filter null values out
 .forEach(stringDoubleEntry -> stringDoubleEntry.setValue(stringDoubleEntry.getValue() * 2)); //multiply values which are not null

In case you need a second map where just values in which are not null just use the forEach to put them into your new map.

answered 31 mins ago

CodeMatrix

8251519

1

This solution does what the OP's code does in a nice form (though stringDoubleEntry is a bit unaccustomedly long). It exploits that the entries are backed by the map; no new map is created.
â€“Â Joop Eggen
17 mins ago

1

I did not want to criticize, indeed the other way around. There was no upvote and others were already upvoted, despite your solution being straight-forward efficient.
â€“Â Joop Eggen
12 mins ago

My mistake I read over 2 words which were the key that was different haha.
â€“Â CodeMatrix
10 mins ago

add a commentÂ |Â

up vote
2
down vote

It can be done like that

someMap.entrySet().stream()
 .filter(stringDoubleEntry -> stringDoubleEntry.getValue() != null) //filter null values out
 .forEach(stringDoubleEntry -> stringDoubleEntry.setValue(stringDoubleEntry.getValue() * 2)); //multiply values which are not null

In case you need a second map where just values in which are not null just use the forEach to put them into your new map.

answered 31 mins ago

CodeMatrix

8251519

1

This solution does what the OP's code does in a nice form (though stringDoubleEntry is a bit unaccustomedly long). It exploits that the entries are backed by the map; no new map is created.
â€“Â Joop Eggen
17 mins ago

1

I did not want to criticize, indeed the other way around. There was no upvote and others were already upvoted, despite your solution being straight-forward efficient.
â€“Â Joop Eggen
12 mins ago

My mistake I read over 2 words which were the key that was different haha.
â€“Â CodeMatrix
10 mins ago

add a commentÂ |Â

up vote
2
down vote

It can be done like that

someMap.entrySet().stream()
 .filter(stringDoubleEntry -> stringDoubleEntry.getValue() != null) //filter null values out
 .forEach(stringDoubleEntry -> stringDoubleEntry.setValue(stringDoubleEntry.getValue() * 2)); //multiply values which are not null

In case you need a second map where just values in which are not null just use the forEach to put them into your new map.

answered 31 mins ago

CodeMatrix

8251519

It can be done like that

someMap.entrySet().stream()
 .filter(stringDoubleEntry -> stringDoubleEntry.getValue() != null) //filter null values out
 .forEach(stringDoubleEntry -> stringDoubleEntry.setValue(stringDoubleEntry.getValue() * 2)); //multiply values which are not null

In case you need a second map where just values in which are not null just use the forEach to put them into your new map.

answered 31 mins ago

CodeMatrix

8251519

answered 31 mins ago

CodeMatrix

8251519

answered 31 mins ago

CodeMatrix

8251519

answered 31 mins ago

CodeMatrix

8251519

1

This solution does what the OP's code does in a nice form (though stringDoubleEntry is a bit unaccustomedly long). It exploits that the entries are backed by the map; no new map is created.
â€“Â Joop Eggen
17 mins ago

1

I did not want to criticize, indeed the other way around. There was no upvote and others were already upvoted, despite your solution being straight-forward efficient.
â€“Â Joop Eggen
12 mins ago

My mistake I read over 2 words which were the key that was different haha.
â€“Â CodeMatrix
10 mins ago

add a commentÂ |Â

1

This solution does what the OP's code does in a nice form (though stringDoubleEntry is a bit unaccustomedly long). It exploits that the entries are backed by the map; no new map is created.
â€“Â Joop Eggen
17 mins ago

1

I did not want to criticize, indeed the other way around. There was no upvote and others were already upvoted, despite your solution being straight-forward efficient.
â€“Â Joop Eggen
12 mins ago

My mistake I read over 2 words which were the key that was different haha.
â€“Â CodeMatrix
10 mins ago

This solution does what the OP's code does in a nice form (though stringDoubleEntry is a bit unaccustomedly long). It exploits that the entries are backed by the map; no new map is created.
â€“Â Joop Eggen
17 mins ago

I did not want to criticize, indeed the other way around. There was no upvote and others were already upvoted, despite your solution being straight-forward efficient.
â€“Â Joop Eggen
12 mins ago

My mistake I read over 2 words which were the key that was different haha.
â€“Â CodeMatrix
10 mins ago

add a commentÂ |Â

up vote
2
down vote

You can achieve that by converting into a stream, something like:

 someMap.entrySet()
 .forEach(entry -> 
 if(entry.getValue() != null) 
 adjustedMap.put(entry.getKey(), someMap.get(entry.getKey()) * 2);
 else 
 adjustedMap.put(entry.getKey(), null);
 
 );

which can be shorted to :

someMap.forEach((key, value) -> 
 if (value != null) 
 adjustedMap.put(key, value * 2);
 else 
 adjustedMap.put(key, null);
 
 );

So, if you'r having a map with:

Map<String, Double> someMap = new HashMap<>();
someMap.put("test1", 1d);
someMap.put("test2", 2d);
someMap.put("test3", 3d);
someMap.put("testNull", null);
someMap.put("test4", 4d);

You will get this output:

test4=8.0, test2=4.0, test3=6.0, testNull=null, test1=2.0

edited 2 mins ago

answered 34 mins ago

Leviand

1,3881122

3

The OP wanted to "keep the nulls as nulls.", not filter them out.
â€“Â Eran
22 mins ago

@Eran My bad, i'm fixing, thanks
â€“Â Leviand
21 mins ago

@Eran fixed, thanks for pointing it
â€“Â Leviand
9 mins ago

Your someMap.get(key) can be simply value instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
3 mins ago

add a commentÂ |Â

up vote
2
down vote

You can achieve that by converting into a stream, something like:

 someMap.entrySet()
 .forEach(entry -> 
 if(entry.getValue() != null) 
 adjustedMap.put(entry.getKey(), someMap.get(entry.getKey()) * 2);
 else 
 adjustedMap.put(entry.getKey(), null);
 
 );

which can be shorted to :

someMap.forEach((key, value) -> 
 if (value != null) 
 adjustedMap.put(key, value * 2);
 else 
 adjustedMap.put(key, null);
 
 );

So, if you'r having a map with:

Map<String, Double> someMap = new HashMap<>();
someMap.put("test1", 1d);
someMap.put("test2", 2d);
someMap.put("test3", 3d);
someMap.put("testNull", null);
someMap.put("test4", 4d);

You will get this output:

test4=8.0, test2=4.0, test3=6.0, testNull=null, test1=2.0

edited 2 mins ago

answered 34 mins ago

Leviand

1,3881122

3

The OP wanted to "keep the nulls as nulls.", not filter them out.
â€“Â Eran
22 mins ago

@Eran My bad, i'm fixing, thanks
â€“Â Leviand
21 mins ago

@Eran fixed, thanks for pointing it
â€“Â Leviand
9 mins ago

Your someMap.get(key) can be simply value instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
3 mins ago

add a commentÂ |Â

up vote
2
down vote

You can achieve that by converting into a stream, something like:

 someMap.entrySet()
 .forEach(entry -> 
 if(entry.getValue() != null) 
 adjustedMap.put(entry.getKey(), someMap.get(entry.getKey()) * 2);
 else 
 adjustedMap.put(entry.getKey(), null);
 
 );

which can be shorted to :

someMap.forEach((key, value) -> 
 if (value != null) 
 adjustedMap.put(key, value * 2);
 else 
 adjustedMap.put(key, null);
 
 );

So, if you'r having a map with:

Map<String, Double> someMap = new HashMap<>();
someMap.put("test1", 1d);
someMap.put("test2", 2d);
someMap.put("test3", 3d);
someMap.put("testNull", null);
someMap.put("test4", 4d);

You will get this output:

test4=8.0, test2=4.0, test3=6.0, testNull=null, test1=2.0

edited 2 mins ago

answered 34 mins ago

Leviand

1,3881122

You can achieve that by converting into a stream, something like:

 someMap.entrySet()
 .forEach(entry -> 
 if(entry.getValue() != null) 
 adjustedMap.put(entry.getKey(), someMap.get(entry.getKey()) * 2);
 else 
 adjustedMap.put(entry.getKey(), null);
 
 );

which can be shorted to :

someMap.forEach((key, value) -> 
 if (value != null) 
 adjustedMap.put(key, value * 2);
 else 
 adjustedMap.put(key, null);
 
 );

So, if you'r having a map with:

Map<String, Double> someMap = new HashMap<>();
someMap.put("test1", 1d);
someMap.put("test2", 2d);
someMap.put("test3", 3d);
someMap.put("testNull", null);
someMap.put("test4", 4d);

You will get this output:

test4=8.0, test2=4.0, test3=6.0, testNull=null, test1=2.0

edited 2 mins ago

answered 34 mins ago

Leviand

1,3881122

edited 2 mins ago

answered 34 mins ago

Leviand

1,3881122

answered 34 mins ago

Leviand

1,3881122

answered 34 mins ago

Leviand

1,3881122

3

The OP wanted to "keep the nulls as nulls.", not filter them out.
â€“Â Eran
22 mins ago

@Eran My bad, i'm fixing, thanks
â€“Â Leviand
21 mins ago

@Eran fixed, thanks for pointing it
â€“Â Leviand
9 mins ago

Your someMap.get(key) can be simply value instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
3 mins ago

add a commentÂ |Â

3

The OP wanted to "keep the nulls as nulls.", not filter them out.
â€“Â Eran
22 mins ago

@Eran My bad, i'm fixing, thanks
â€“Â Leviand
21 mins ago

@Eran fixed, thanks for pointing it
â€“Â Leviand
9 mins ago

Your someMap.get(key) can be simply value instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
3 mins ago

The OP wanted to "keep the nulls as nulls.", not filter them out.
â€“Â Eran
22 mins ago

@Eran My bad, i'm fixing, thanks
â€“Â Leviand
21 mins ago

@Eran fixed, thanks for pointing it
â€“Â Leviand
9 mins ago

Your someMap.get(key) can be simply value instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
3 mins ago

add a commentÂ |Â

up vote
1
down vote

Use like this.

 Map<String, Double> adjustedMap = map.entrySet().stream()filter(x -> x.getValue() != null)
 .collect(Collectors.toMap(x -> x.getKey(), x -> 2*x.getValue()));
 //printing 
 adjustedMap.entrySet().stream().forEach(System.out::println);

edited 23 mins ago

answered 30 mins ago

amitpandey

158111

This is not null safe
â€“Â Eran
26 mins ago

add a commentÂ |Â

up vote
1
down vote

Use like this.

 Map<String, Double> adjustedMap = map.entrySet().stream()filter(x -> x.getValue() != null)
 .collect(Collectors.toMap(x -> x.getKey(), x -> 2*x.getValue()));
 //printing 
 adjustedMap.entrySet().stream().forEach(System.out::println);

edited 23 mins ago

answered 30 mins ago

amitpandey

158111

This is not null safe
â€“Â Eran
26 mins ago

add a commentÂ |Â

up vote
1
down vote

Use like this.

 Map<String, Double> adjustedMap = map.entrySet().stream()filter(x -> x.getValue() != null)
 .collect(Collectors.toMap(x -> x.getKey(), x -> 2*x.getValue()));
 //printing 
 adjustedMap.entrySet().stream().forEach(System.out::println);

edited 23 mins ago

answered 30 mins ago

amitpandey

158111

Use like this.

 Map<String, Double> adjustedMap = map.entrySet().stream()filter(x -> x.getValue() != null)
 .collect(Collectors.toMap(x -> x.getKey(), x -> 2*x.getValue()));
 //printing 
 adjustedMap.entrySet().stream().forEach(System.out::println);

edited 23 mins ago

answered 30 mins ago

amitpandey

158111

edited 23 mins ago

answered 30 mins ago

amitpandey

158111

answered 30 mins ago

amitpandey

158111

answered 30 mins ago

amitpandey

158111

This is not null safe
â€“Â Eran
26 mins ago

add a commentÂ |Â

This is not null safe
â€“Â Eran
26 mins ago

This is not null safe
â€“Â Eran
26 mins ago

add a commentÂ |Â

up vote
1
down vote

You can do this with this code:

 Map<String, Double> map = new HashMap<>();
 map.put("1", 3.0);
 map.put("3", null);
 map.put("2", 5.0);

 Map<String, Double> res = map.entrySet().stream()
 .collect(HashMap::new, (m,v)->m.put(v.getKey(), v.getValue() != null ? v.getValue() * 2 : null), HashMap::putAll);

 System.out.println(res);

and the output will be:

1=6.0, 2=10.0, 3=null

It will allow you to keep null values in the map.

edited 18 mins ago

answered 24 mins ago

user987339

7,86862936

add a commentÂ |Â

up vote
1
down vote

You can do this with this code:

 Map<String, Double> map = new HashMap<>();
 map.put("1", 3.0);
 map.put("3", null);
 map.put("2", 5.0);

 Map<String, Double> res = map.entrySet().stream()
 .collect(HashMap::new, (m,v)->m.put(v.getKey(), v.getValue() != null ? v.getValue() * 2 : null), HashMap::putAll);

 System.out.println(res);

and the output will be:

1=6.0, 2=10.0, 3=null

It will allow you to keep null values in the map.

edited 18 mins ago

answered 24 mins ago

user987339

7,86862936

add a commentÂ |Â

up vote
1
down vote

You can do this with this code:

 Map<String, Double> map = new HashMap<>();
 map.put("1", 3.0);
 map.put("3", null);
 map.put("2", 5.0);

 Map<String, Double> res = map.entrySet().stream()
 .collect(HashMap::new, (m,v)->m.put(v.getKey(), v.getValue() != null ? v.getValue() * 2 : null), HashMap::putAll);

 System.out.println(res);

and the output will be:

1=6.0, 2=10.0, 3=null

It will allow you to keep null values in the map.

edited 18 mins ago

answered 24 mins ago

user987339

7,86862936

You can do this with this code:

 Map<String, Double> map = new HashMap<>();
 map.put("1", 3.0);
 map.put("3", null);
 map.put("2", 5.0);

 Map<String, Double> res = map.entrySet().stream()
 .collect(HashMap::new, (m,v)->m.put(v.getKey(), v.getValue() != null ? v.getValue() * 2 : null), HashMap::putAll);

 System.out.println(res);

and the output will be:

1=6.0, 2=10.0, 3=null

It will allow you to keep null values in the map.

edited 18 mins ago

answered 24 mins ago

user987339

7,86862936

edited 18 mins ago

answered 24 mins ago

user987339

7,86862936

answered 24 mins ago

user987339

7,86862936

answered 24 mins ago

user987339

7,86862936

add a commentÂ |Â

up vote
1
down vote

To keep null values you can use something as simple as :

someMap.keySet()
 .stream()
 .forEach(key -> adjustedMap.put(key, (someMap.get(key)) == null ? null : someMap.get(key) * 2));

answered 18 mins ago

c0der

7,31241643

You should absolutely stream on the entrySet(), they you'd avoid calling someMap.get(key) in a loop, and would be able to just do entry.value() instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
5 mins ago

add a commentÂ |Â

up vote
1
down vote

To keep null values you can use something as simple as :

someMap.keySet()
 .stream()
 .forEach(key -> adjustedMap.put(key, (someMap.get(key)) == null ? null : someMap.get(key) * 2));

answered 18 mins ago

c0der

7,31241643

You should absolutely stream on the entrySet(), they you'd avoid calling someMap.get(key) in a loop, and would be able to just do entry.value() instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
5 mins ago

add a commentÂ |Â

up vote
1
down vote

To keep null values you can use something as simple as :

someMap.keySet()
 .stream()
 .forEach(key -> adjustedMap.put(key, (someMap.get(key)) == null ? null : someMap.get(key) * 2));

answered 18 mins ago

c0der

7,31241643

To keep null values you can use something as simple as :

someMap.keySet()
 .stream()
 .forEach(key -> adjustedMap.put(key, (someMap.get(key)) == null ? null : someMap.get(key) * 2));

answered 18 mins ago

c0der

7,31241643

answered 18 mins ago

c0der

7,31241643

answered 18 mins ago

c0der

7,31241643

answered 18 mins ago

c0der

7,31241643

You should absolutely stream on the entrySet(), they you'd avoid calling someMap.get(key) in a loop, and would be able to just do entry.value() instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
5 mins ago

add a commentÂ |Â

You should absolutely stream on the entrySet(), they you'd avoid calling someMap.get(key) in a loop, and would be able to just do entry.value() instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
5 mins ago

You should absolutely stream on the entrySet(), they you'd avoid calling someMap.get(key) in a loop, and would be able to just do entry.value() instead. Anyway, downvoting for style. It may be my personal subjective preference, but I strongly believe functional code should be side-effect free. Therefore, using forEach() on one map to change a different map is a no-no in my book. I'd prefer collecting the stream into a new map instead. That's the canonical and recognized way of consuming streams.
â€“Â Petr JaneÃ„Âek
5 mins ago

add a commentÂ |Â

up vote
1
down vote

Try something like this with java 8 steam api

Map<String, Double> newMap = oldMap.entrySet().stream()
 .collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue() == null ? null: x.getValue()*2));

edited 14 mins ago

Nicholas K

2,6502725

answered 27 mins ago

oguzhan aygun

3018

This will throw NullPointerException for any null values.
â€“Â Eran
24 mins ago

how is it possible ?
â€“Â oguzhan aygun
22 mins ago

3

That's the behavior of Collectors.toMap. You can try it and see for yourself.
â€“Â Eran
20 mins ago

thank you Eran I just tried and learn something new :)
â€“Â oguzhan aygun
14 mins ago

add a commentÂ |Â

up vote
1
down vote

Try something like this with java 8 steam api

Map<String, Double> newMap = oldMap.entrySet().stream()
 .collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue() == null ? null: x.getValue()*2));

edited 14 mins ago

Nicholas K

2,6502725

answered 27 mins ago

oguzhan aygun

3018

This will throw NullPointerException for any null values.
â€“Â Eran
24 mins ago

how is it possible ?
â€“Â oguzhan aygun
22 mins ago

3

That's the behavior of Collectors.toMap. You can try it and see for yourself.
â€“Â Eran
20 mins ago

thank you Eran I just tried and learn something new :)
â€“Â oguzhan aygun
14 mins ago

add a commentÂ |Â

up vote
1
down vote

Try something like this with java 8 steam api

Map<String, Double> newMap = oldMap.entrySet().stream()
 .collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue() == null ? null: x.getValue()*2));

edited 14 mins ago

Nicholas K

2,6502725

answered 27 mins ago

oguzhan aygun

3018

Try something like this with java 8 steam api

Map<String, Double> newMap = oldMap.entrySet().stream()
 .collect(Collectors.toMap(x -> x.getKey(), x -> x.getValue() == null ? null: x.getValue()*2));

edited 14 mins ago

Nicholas K

2,6502725

answered 27 mins ago

oguzhan aygun

3018

edited 14 mins ago

Nicholas K

2,6502725

edited 14 mins ago

Nicholas K

2,6502725

edited 14 mins ago

Nicholas K

2,6502725

answered 27 mins ago

oguzhan aygun

3018

answered 27 mins ago

oguzhan aygun

3018

answered 27 mins ago

oguzhan aygun

3018

This will throw NullPointerException for any null values.
â€“Â Eran
24 mins ago

how is it possible ?
â€“Â oguzhan aygun
22 mins ago

3

That's the behavior of Collectors.toMap. You can try it and see for yourself.
â€“Â Eran
20 mins ago

thank you Eran I just tried and learn something new :)
â€“Â oguzhan aygun
14 mins ago

add a commentÂ |Â

This will throw NullPointerException for any null values.
â€“Â Eran
24 mins ago

how is it possible ?
â€“Â oguzhan aygun
22 mins ago

3

That's the behavior of Collectors.toMap. You can try it and see for yourself.
â€“Â Eran
20 mins ago

thank you Eran I just tried and learn something new :)
â€“Â oguzhan aygun
14 mins ago

This will throw NullPointerException for any null values.
â€“Â Eran
24 mins ago

how is it possible ?
â€“Â oguzhan aygun
22 mins ago

That's the behavior of Collectors.toMap. You can try it and see for yourself.
â€“Â Eran
20 mins ago

thank you Eran I just tried and learn something new :)
â€“Â oguzhan aygun
14 mins ago

add a commentÂ |Â

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