Repeated replacing elements in the list

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1
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I have a large list of the following form

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1

and I want to combine all of the pairs x->y that share the same x value by adding up their y values. For the above example I want to have

 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

and I want to do it using patterns and ReplaceRepeated command. I tried the following code:

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //.HoldPattern[x_ -> y_, a___, x_ -> z_] -> x -> y + z, a

Can anybody tell me why above code is not working and how can I do it using rules?

asked 1 hour ago

The Legend of 1991

New contributor

1

//. is not really intended for combinations like these. Try Merge: Normal[Merge[1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1, Total]]
â€“Â J. M. is somewhat okay.â™¦
1 hour ago

Thanks @J.M.issomewhatokay. You answer is correct. However, I mostly want to learn about patterns and I wanna know how can extract such patterns.
â€“Â The Legend of 1991
1 hour ago

add a commentÂ |Â

up vote
1
down vote

favorite

I have a large list of the following form

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1

and I want to combine all of the pairs x->y that share the same x value by adding up their y values. For the above example I want to have

 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

and I want to do it using patterns and ReplaceRepeated command. I tried the following code:

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //.HoldPattern[x_ -> y_, a___, x_ -> z_] -> x -> y + z, a

Can anybody tell me why above code is not working and how can I do it using rules?

asked 1 hour ago

The Legend of 1991

New contributor

1

//. is not really intended for combinations like these. Try Merge: Normal[Merge[1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1, Total]]
â€“Â J. M. is somewhat okay.â™¦
1 hour ago

Thanks @J.M.issomewhatokay. You answer is correct. However, I mostly want to learn about patterns and I wanna know how can extract such patterns.
â€“Â The Legend of 1991
1 hour ago

add a commentÂ |Â

up vote
1
down vote

favorite

I have a large list of the following form

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1

and I want to combine all of the pairs x->y that share the same x value by adding up their y values. For the above example I want to have

 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

and I want to do it using patterns and ReplaceRepeated command. I tried the following code:

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //.HoldPattern[x_ -> y_, a___, x_ -> z_] -> x -> y + z, a

Can anybody tell me why above code is not working and how can I do it using rules?

asked 1 hour ago

The Legend of 1991

New contributor

I have a large list of the following form

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1

and I want to combine all of the pairs x->y that share the same x value by adding up their y values. For the above example I want to have

 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

and I want to do it using patterns and ReplaceRepeated command. I tried the following code:

 1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //.HoldPattern[x_ -> y_, a___, x_ -> z_] -> x -> y + z, a

Can anybody tell me why above code is not working and how can I do it using rules?

pattern-matching replacement

asked 1 hour ago

The Legend of 1991

New contributor

asked 1 hour ago

The Legend of 1991

New contributor

asked 1 hour ago

The Legend of 1991

New contributor

asked 1 hour ago

The Legend of 1991

asked 1 hour ago

The Legend of 1991

New contributor

The Legend of 1991 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

1

//. is not really intended for combinations like these. Try Merge: Normal[Merge[1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1, Total]]
â€“Â J. M. is somewhat okay.â™¦
1 hour ago

Thanks @J.M.issomewhatokay. You answer is correct. However, I mostly want to learn about patterns and I wanna know how can extract such patterns.
â€“Â The Legend of 1991
1 hour ago

add a commentÂ |Â

1

//. is not really intended for combinations like these. Try Merge: Normal[Merge[1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1, Total]]
â€“Â J. M. is somewhat okay.â™¦
1 hour ago

Thanks @J.M.issomewhatokay. You answer is correct. However, I mostly want to learn about patterns and I wanna know how can extract such patterns.
â€“Â The Legend of 1991
1 hour ago

//. is not really intended for combinations like these. Try Merge: Normal[Merge[1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1, Total]]
â€“Â J. M. is somewhat okay.â™¦
1 hour ago

Thanks @J.M.issomewhatokay. You answer is correct. However, I mostly want to learn about patterns and I wanna know how can extract such patterns.
â€“Â The Legend of 1991
1 hour ago

add a commentÂ |Â

2 Answers
2

active

oldest

votes

up vote
1
down vote

accepted

In general, there may (or may not) be preceding, intervening, and subsequent elements in the list that must handled using BlankNullSequence

1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //. start___, 
 x_ -> y1_, middle___, x_ -> y2_, end___ :> start, x -> y1 + y2, middle, end

(* 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1 *)

answered 55 mins ago

Bob Hanlon

55.8k23589

Because it is only coincidental that the first element of your list is one of interest (i.e., matching LHS of rule). In general, any number of non-matching elements could be at the start.
â€“Â Bob Hanlon
35 mins ago

Thanks Bob! I am still having problem with start and end. As a related question can you please tell me why for instance Cases[1, 2, 6, 3, 4, 8, 5, x_, y_, z_ /; (y > Max[x, z]):>y] command doesn't return the y values that are greater than their neighbors in the list?
â€“Â The Legend of 1991
15 mins ago

add a commentÂ |Â

up vote
1
down vote

You could use GroupBy:

Normal @ GroupBy[
 1,2->-1,1,1->1,1,2->-1,1,6->1,
 First -> Last,
 Total
]

1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

answered 50 mins ago

Carl Woll

59k277152

add a commentÂ |Â

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

up vote
1
down vote

accepted

In general, there may (or may not) be preceding, intervening, and subsequent elements in the list that must handled using BlankNullSequence

1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //. start___, 
 x_ -> y1_, middle___, x_ -> y2_, end___ :> start, x -> y1 + y2, middle, end

(* 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1 *)

answered 55 mins ago

Bob Hanlon

55.8k23589

Because it is only coincidental that the first element of your list is one of interest (i.e., matching LHS of rule). In general, any number of non-matching elements could be at the start.
â€“Â Bob Hanlon
35 mins ago

Thanks Bob! I am still having problem with start and end. As a related question can you please tell me why for instance Cases[1, 2, 6, 3, 4, 8, 5, x_, y_, z_ /; (y > Max[x, z]):>y] command doesn't return the y values that are greater than their neighbors in the list?
â€“Â The Legend of 1991
15 mins ago

add a commentÂ |Â

up vote
1
down vote

accepted

In general, there may (or may not) be preceding, intervening, and subsequent elements in the list that must handled using BlankNullSequence

1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //. start___, 
 x_ -> y1_, middle___, x_ -> y2_, end___ :> start, x -> y1 + y2, middle, end

(* 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1 *)

answered 55 mins ago

Bob Hanlon

55.8k23589

Because it is only coincidental that the first element of your list is one of interest (i.e., matching LHS of rule). In general, any number of non-matching elements could be at the start.
â€“Â Bob Hanlon
35 mins ago

Thanks Bob! I am still having problem with start and end. As a related question can you please tell me why for instance Cases[1, 2, 6, 3, 4, 8, 5, x_, y_, z_ /; (y > Max[x, z]):>y] command doesn't return the y values that are greater than their neighbors in the list?
â€“Â The Legend of 1991
15 mins ago

add a commentÂ |Â

up vote
1
down vote

accepted

In general, there may (or may not) be preceding, intervening, and subsequent elements in the list that must handled using BlankNullSequence

1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //. start___, 
 x_ -> y1_, middle___, x_ -> y2_, end___ :> start, x -> y1 + y2, middle, end

(* 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1 *)

answered 55 mins ago

Bob Hanlon

55.8k23589

In general, there may (or may not) be preceding, intervening, and subsequent elements in the list that must handled using BlankNullSequence

1, 2 -> -1, 1, 1 -> 1, 1, 2 -> -1, 1, 6 -> 1 //. start___, 
 x_ -> y1_, middle___, x_ -> y2_, end___ :> start, x -> y1 + y2, middle, end

(* 1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1 *)

answered 55 mins ago

Bob Hanlon

55.8k23589

answered 55 mins ago

Bob Hanlon

55.8k23589

answered 55 mins ago

Bob Hanlon

55.8k23589

answered 55 mins ago

Bob Hanlon

55.8k23589

Because it is only coincidental that the first element of your list is one of interest (i.e., matching LHS of rule). In general, any number of non-matching elements could be at the start.
â€“Â Bob Hanlon
35 mins ago

Thanks Bob! I am still having problem with start and end. As a related question can you please tell me why for instance Cases[1, 2, 6, 3, 4, 8, 5, x_, y_, z_ /; (y > Max[x, z]):>y] command doesn't return the y values that are greater than their neighbors in the list?
â€“Â The Legend of 1991
15 mins ago

add a commentÂ |Â

Because it is only coincidental that the first element of your list is one of interest (i.e., matching LHS of rule). In general, any number of non-matching elements could be at the start.
â€“Â Bob Hanlon
35 mins ago

Thanks Bob! I am still having problem with start and end. As a related question can you please tell me why for instance Cases[1, 2, 6, 3, 4, 8, 5, x_, y_, z_ /; (y > Max[x, z]):>y] command doesn't return the y values that are greater than their neighbors in the list?
â€“Â The Legend of 1991
15 mins ago

Because it is only coincidental that the first element of your list is one of interest (i.e., matching LHS of rule). In general, any number of non-matching elements could be at the start.
â€“Â Bob Hanlon
35 mins ago

Thanks Bob! I am still having problem with start and end. As a related question can you please tell me why for instance Cases[1, 2, 6, 3, 4, 8, 5, x_, y_, z_ /; (y > Max[x, z]):>y] command doesn't return the y values that are greater than their neighbors in the list?
â€“Â The Legend of 1991
15 mins ago

add a commentÂ |Â

up vote
1
down vote

You could use GroupBy:

Normal @ GroupBy[
 1,2->-1,1,1->1,1,2->-1,1,6->1,
 First -> Last,
 Total
]

1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

answered 50 mins ago

Carl Woll

59k277152

add a commentÂ |Â

up vote
1
down vote

You could use GroupBy:

Normal @ GroupBy[
 1,2->-1,1,1->1,1,2->-1,1,6->1,
 First -> Last,
 Total
]

1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

answered 50 mins ago

Carl Woll

59k277152

add a commentÂ |Â

up vote
1
down vote

You could use GroupBy:

Normal @ GroupBy[
 1,2->-1,1,1->1,1,2->-1,1,6->1,
 First -> Last,
 Total
]

1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

answered 50 mins ago

Carl Woll

59k277152

You could use GroupBy:

Normal @ GroupBy[
 1,2->-1,1,1->1,1,2->-1,1,6->1,
 First -> Last,
 Total
]

1, 2 -> -2, 1, 1 -> 1, 1, 6 -> 1

answered 50 mins ago

Carl Woll

59k277152

answered 50 mins ago

Carl Woll

59k277152

answered 50 mins ago

Carl Woll

59k277152

answered 50 mins ago

Carl Woll

59k277152

add a commentÂ |Â

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