Using DeleteCases to match a string pattern

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3
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I am trying to remove all of the elements from a list that contain the characters "err" in that order.

I expect the following code to return an empty list:

DeleteCases["Aerr", __ ~~ "err"]

However it fails to recognize the pattern and will return the full List. What am I missing in the documentation for patterns? Perhaps it is an issue with DeleteCases, as I can use StringMatchQ to identify that the patterns match.

StringMatchQ["Aerr", __ ~~ "err"]

Returns True.

edited 21 mins ago

Carl Woll

63.3k282163

asked 36 mins ago

Karl

163

New contributor

add a commentÂ |Â

up vote
3
down vote

favorite

I am trying to remove all of the elements from a list that contain the characters "err" in that order.

I expect the following code to return an empty list:

DeleteCases["Aerr", __ ~~ "err"]

StringMatchQ["Aerr", __ ~~ "err"]

Returns True.

edited 21 mins ago

Carl Woll

63.3k282163

asked 36 mins ago

Karl

163

New contributor

add a commentÂ |Â

up vote
3
down vote

favorite

I am trying to remove all of the elements from a list that contain the characters "err" in that order.

I expect the following code to return an empty list:

DeleteCases["Aerr", __ ~~ "err"]

StringMatchQ["Aerr", __ ~~ "err"]

Returns True.

edited 21 mins ago

Carl Woll

63.3k282163

asked 36 mins ago

Karl

163

New contributor

I am trying to remove all of the elements from a list that contain the characters "err" in that order.

I expect the following code to return an empty list:

DeleteCases["Aerr", __ ~~ "err"]

StringMatchQ["Aerr", __ ~~ "err"]

Returns True.

pattern-matching filtering

edited 21 mins ago

Carl Woll

63.3k282163

asked 36 mins ago

Karl

163

New contributor

edited 21 mins ago

Carl Woll

63.3k282163

asked 36 mins ago

Karl

163

New contributor

edited 21 mins ago

Carl Woll

63.3k282163

edited 21 mins ago

Carl Woll

63.3k282163

edited 21 mins ago

Carl Woll

63.3k282163

asked 36 mins ago

Karl

163

New contributor

asked 36 mins ago

Karl

163

asked 36 mins ago

Karl

163

New contributor

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

add a commentÂ |Â

2 Answers
2

active

oldest

votes

up vote
4
down vote

First note the FullForm of your pattern:

__ ~~ "err" //FullForm

StringExpression[BlankSequence,"err"]

The pattern is a StringExpression, so you must use a string function, e.g., StringMatchQ instead of DeleteCases, which is expecting a normal pattern. Here are some other possibilities:

list = "Aerr";

Select[list, Not @* StringMatchQ[__ ~~ "err"]]
Pick[list, StringMatchQ[list, __ ~~ "err"], False]

answered 17 mins ago

Carl Woll

63.3k282163

add a commentÂ |Â

up vote
2
down vote

DeleteCases["Aerr", _?(StringMatchQ[ "*err"]) ]

For versions prior to version 10:

DeleteCases["Aerr", _?(StringMatchQ[#, "*err"] &)]

edited 19 mins ago

answered 32 mins ago

kglr

168k8192395

While I appreciate the working example, I would have loved further explanation of how it works. I've gathered that the "?" syntax is a pattern test, but how does the "_" pattern which is for a single character match "Aerr"? Also, is it a bug that the code in my original question didn't work, or a misunderstanding of how to use patterns?
â€“Â Karl
16 mins ago

@Karl, please see Carl' Woll's answer for a detailed explanation.
â€“Â kglr
12 mins ago

1

@Karl, _ pattern matches any Mathematica expression; only in string patterns it stands for a single character.
â€“Â kglr
6 mins ago

add a commentÂ |Â

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2 Answers
2

active

oldest

votes

2 Answers
2

active

oldest

votes

up vote
4
down vote

First note the FullForm of your pattern:

__ ~~ "err" //FullForm

StringExpression[BlankSequence,"err"]

The pattern is a StringExpression, so you must use a string function, e.g., StringMatchQ instead of DeleteCases, which is expecting a normal pattern. Here are some other possibilities:

list = "Aerr";

Select[list, Not @* StringMatchQ[__ ~~ "err"]]
Pick[list, StringMatchQ[list, __ ~~ "err"], False]

answered 17 mins ago

Carl Woll

63.3k282163

add a commentÂ |Â

up vote
4
down vote

First note the FullForm of your pattern:

__ ~~ "err" //FullForm

StringExpression[BlankSequence,"err"]

The pattern is a StringExpression, so you must use a string function, e.g., StringMatchQ instead of DeleteCases, which is expecting a normal pattern. Here are some other possibilities:

list = "Aerr";

Select[list, Not @* StringMatchQ[__ ~~ "err"]]
Pick[list, StringMatchQ[list, __ ~~ "err"], False]

answered 17 mins ago

Carl Woll

63.3k282163

add a commentÂ |Â

up vote
4
down vote

First note the FullForm of your pattern:

__ ~~ "err" //FullForm

StringExpression[BlankSequence,"err"]

The pattern is a StringExpression, so you must use a string function, e.g., StringMatchQ instead of DeleteCases, which is expecting a normal pattern. Here are some other possibilities:

list = "Aerr";

Select[list, Not @* StringMatchQ[__ ~~ "err"]]
Pick[list, StringMatchQ[list, __ ~~ "err"], False]

answered 17 mins ago

Carl Woll

63.3k282163

First note the FullForm of your pattern:

__ ~~ "err" //FullForm

StringExpression[BlankSequence,"err"]

The pattern is a StringExpression, so you must use a string function, e.g., StringMatchQ instead of DeleteCases, which is expecting a normal pattern. Here are some other possibilities:

list = "Aerr";

Select[list, Not @* StringMatchQ[__ ~~ "err"]]
Pick[list, StringMatchQ[list, __ ~~ "err"], False]

answered 17 mins ago

Carl Woll

63.3k282163

answered 17 mins ago

Carl Woll

63.3k282163

answered 17 mins ago

Carl Woll

63.3k282163

answered 17 mins ago

Carl Woll

63.3k282163

add a commentÂ |Â

up vote
2
down vote

DeleteCases["Aerr", _?(StringMatchQ[ "*err"]) ]

For versions prior to version 10:

DeleteCases["Aerr", _?(StringMatchQ[#, "*err"] &)]

edited 19 mins ago

answered 32 mins ago

kglr

168k8192395

While I appreciate the working example, I would have loved further explanation of how it works. I've gathered that the "?" syntax is a pattern test, but how does the "_" pattern which is for a single character match "Aerr"? Also, is it a bug that the code in my original question didn't work, or a misunderstanding of how to use patterns?
â€“Â Karl
16 mins ago

@Karl, please see Carl' Woll's answer for a detailed explanation.
â€“Â kglr
12 mins ago

1

@Karl, _ pattern matches any Mathematica expression; only in string patterns it stands for a single character.
â€“Â kglr
6 mins ago

add a commentÂ |Â

up vote
2
down vote

DeleteCases["Aerr", _?(StringMatchQ[ "*err"]) ]

For versions prior to version 10:

DeleteCases["Aerr", _?(StringMatchQ[#, "*err"] &)]

edited 19 mins ago

answered 32 mins ago

kglr

168k8192395

While I appreciate the working example, I would have loved further explanation of how it works. I've gathered that the "?" syntax is a pattern test, but how does the "_" pattern which is for a single character match "Aerr"? Also, is it a bug that the code in my original question didn't work, or a misunderstanding of how to use patterns?
â€“Â Karl
16 mins ago

@Karl, please see Carl' Woll's answer for a detailed explanation.
â€“Â kglr
12 mins ago

1

@Karl, _ pattern matches any Mathematica expression; only in string patterns it stands for a single character.
â€“Â kglr
6 mins ago

add a commentÂ |Â

up vote
2
down vote

DeleteCases["Aerr", _?(StringMatchQ[ "*err"]) ]

For versions prior to version 10:

DeleteCases["Aerr", _?(StringMatchQ[#, "*err"] &)]

edited 19 mins ago

answered 32 mins ago

kglr

168k8192395

DeleteCases["Aerr", _?(StringMatchQ[ "*err"]) ]

For versions prior to version 10:

DeleteCases["Aerr", _?(StringMatchQ[#, "*err"] &)]

edited 19 mins ago

answered 32 mins ago

kglr

168k8192395

edited 19 mins ago

answered 32 mins ago

kglr

168k8192395

answered 32 mins ago

kglr

168k8192395

answered 32 mins ago

kglr

168k8192395

While I appreciate the working example, I would have loved further explanation of how it works. I've gathered that the "?" syntax is a pattern test, but how does the "_" pattern which is for a single character match "Aerr"? Also, is it a bug that the code in my original question didn't work, or a misunderstanding of how to use patterns?
â€“Â Karl
16 mins ago

@Karl, please see Carl' Woll's answer for a detailed explanation.
â€“Â kglr
12 mins ago

1

@Karl, _ pattern matches any Mathematica expression; only in string patterns it stands for a single character.
â€“Â kglr
6 mins ago

add a commentÂ |Â

While I appreciate the working example, I would have loved further explanation of how it works. I've gathered that the "?" syntax is a pattern test, but how does the "_" pattern which is for a single character match "Aerr"? Also, is it a bug that the code in my original question didn't work, or a misunderstanding of how to use patterns?
â€“Â Karl
16 mins ago

@Karl, please see Carl' Woll's answer for a detailed explanation.
â€“Â kglr
12 mins ago

1

@Karl, _ pattern matches any Mathematica expression; only in string patterns it stands for a single character.
â€“Â kglr
6 mins ago

While I appreciate the working example, I would have loved further explanation of how it works. I've gathered that the "?" syntax is a pattern test, but how does the "_" pattern which is for a single character match "Aerr"? Also, is it a bug that the code in my original question didn't work, or a misunderstanding of how to use patterns?
â€“Â Karl
16 mins ago

@Karl, please see Carl' Woll's answer for a detailed explanation.
â€“Â kglr
12 mins ago

@Karl, _ pattern matches any Mathematica expression; only in string patterns it stands for a single character.
â€“Â kglr
6 mins ago

add a commentÂ |Â

Karl is a new contributor. Be nice, and check out our Code of Conduct.

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