Unexpected behaviour of Nothing inside List inside Association
$begingroup$
When evaluating the following input:
<|a -> {c, d, e}|> /. d -> Nothing
I get (expression 1):
<|a -> {c, Nothing, e}|>
However I would expect to get (expression 2):
<|a -> {c, e}|>
Nevertheless, if i place the cursor on the unexpected output (expression 1) and evaluate it by pressing Shift + Enter, I get the expected output (expression 2), which is even more puzzling.
Mathematica version is 11.0.0.0
Should this behaviour be expected or is it a bug? Why?
list-manipulation replacement associations
asked 2 days ago
darmualdarmual
413
$endgroup$
add a comment |
$begingroup$
When evaluating the following input:
<|a -> {c, d, e}|> /. d -> Nothing
I get (expression 1):
<|a -> {c, Nothing, e}|>
However I would expect to get (expression 2):
<|a -> {c, e}|>
Nevertheless, if i place the cursor on the unexpected output (expression 1) and evaluate it by pressing Shift + Enter, I get the expected output (expression 2), which is even more puzzling.
Mathematica version is 11.0.0.0
Should this behaviour be expected or is it a bug? Why?
list-manipulation replacement associations
asked 2 days ago
darmualdarmual
413
$endgroup$
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
2 days ago
add a comment |
$begingroup$
When evaluating the following input:
<|a -> {c, d, e}|> /. d -> Nothing
I get (expression 1):
<|a -> {c, Nothing, e}|>
However I would expect to get (expression 2):
<|a -> {c, e}|>
Nevertheless, if i place the cursor on the unexpected output (expression 1) and evaluate it by pressing Shift + Enter, I get the expected output (expression 2), which is even more puzzling.
Mathematica version is 11.0.0.0
Should this behaviour be expected or is it a bug? Why?
list-manipulation replacement associations
asked 2 days ago
darmualdarmual
413
$endgroup$
When evaluating the following input:
<|a -> {c, d, e}|> /. d -> Nothing
I get (expression 1):
<|a -> {c, Nothing, e}|>
However I would expect to get (expression 2):
<|a -> {c, e}|>
Nevertheless, if i place the cursor on the unexpected output (expression 1) and evaluate it by pressing Shift + Enter, I get the expected output (expression 2), which is even more puzzling.
Mathematica version is 11.0.0.0
Should this behaviour be expected or is it a bug? Why?
list-manipulation replacement associations
list-manipulation replacement associations
asked 2 days ago
darmualdarmual
413
asked 2 days ago
darmualdarmual
413
asked 2 days ago
darmualdarmual
413
asked 2 days ago
darmualdarmual
413
asked 2 days ago
darmualdarmual
413
413
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
2 days ago
add a comment |
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
2 days ago
1
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
2 days ago
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
2 days ago
add a comment |
5 Answers
5
active
oldest
votes
$begingroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
AssociationisHoldAllComplete. Once it is created, its parts will then normally be held unevaluated.
From Nothing>> Details
- Nothing is removed as part of the standard evaluation process. It is not removed in expressions that are held or inactive.
You can Map ReplaceAll on the association to force removal of Nothings:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
answered 2 days ago
kglrkglr
179k9198410
$endgroup$
add a comment |
$begingroup$
Use Replace with level spec All rather than ReplaceAll:
Replace[<|a -> {c, d, e}|>, d -> Nothing, All]
<|a -> {c, e}|>
Related: Is there a difference between Replace with parameter "All" and ReplaceAll
answered 2 days ago
CoolwaterCoolwater
14.8k32553
$endgroup$
add a comment |
$begingroup$
Pattern matching to a function evaluation inside an Association answers your question about bug vs expected result.
This will not do what your input suggests but let me anticipate your needs:
<|a -> {b, c, d}, e :> {d, Print[1], d}, f -> d|> //.
{a___, d, b___} :> {a, b} /. (*this way Print is not evaluated*)
d -> Nothing
<|a -> {b, c}, e :> {Print[1]}, f -> Nothing|>
answered 2 days ago
Kuba♦Kuba
104k12201520
$endgroup$
add a comment |
$begingroup$
For completeness sakes (I believe Coolwater's answer is best):
assoc = Association[ a → {c,d,e} ];
Query
assoc // Query[ All, ReplaceAll[ d → Nothing ] ]
(* <|a -> {c, e}|> *)
Note: This will need repeated use of All for nested associations.
DeleteCases
Before there was Nothing there was DeleteCases and the like:
assoc // DeleteCases[ #, d, Infinity ]&
(* <|a -> {c, e}|> *)
answered 2 days ago
gwrgwr
7,73822558
$endgroup$
add a comment |
$begingroup$
You may use Query to evaluate the result of the replace in an Association. Query gives direct access to the key's value which then evaluated in Query.
Query[All, # /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
Hope this helps.
answered 2 days ago
EdmundEdmund
26.2k330100
$endgroup$
add a comment |
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5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
AssociationisHoldAllComplete. Once it is created, its parts will then normally be held unevaluated.
From Nothing>> Details
- Nothing is removed as part of the standard evaluation process. It is not removed in expressions that are held or inactive.
You can Map ReplaceAll on the association to force removal of Nothings:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
answered 2 days ago
kglrkglr
179k9198410
$endgroup$
add a comment |
$begingroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
AssociationisHoldAllComplete. Once it is created, its parts will then normally be held unevaluated.
From Nothing>> Details
- Nothing is removed as part of the standard evaluation process. It is not removed in expressions that are held or inactive.
You can Map ReplaceAll on the association to force removal of Nothings:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
answered 2 days ago
kglrkglr
179k9198410
$endgroup$
add a comment |
$begingroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
AssociationisHoldAllComplete. Once it is created, its parts will then normally be held unevaluated.
From Nothing>> Details
- Nothing is removed as part of the standard evaluation process. It is not removed in expressions that are held or inactive.
You can Map ReplaceAll on the association to force removal of Nothings:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
answered 2 days ago
kglrkglr
179k9198410
$endgroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
AssociationisHoldAllComplete. Once it is created, its parts will then normally be held unevaluated.
From Nothing>> Details
- Nothing is removed as part of the standard evaluation process. It is not removed in expressions that are held or inactive.
You can Map ReplaceAll on the association to force removal of Nothings:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
answered 2 days ago
kglrkglr
179k9198410
edited 2 days ago
answered 2 days ago
kglrkglr
179k9198410
answered 2 days ago
kglrkglr
179k9198410
answered 2 days ago
kglrkglr
179k9198410
179k9198410
add a comment |
add a comment |
$begingroup$
Use Replace with level spec All rather than ReplaceAll:
Replace[<|a -> {c, d, e}|>, d -> Nothing, All]
<|a -> {c, e}|>
Related: Is there a difference between Replace with parameter "All" and ReplaceAll
answered 2 days ago
CoolwaterCoolwater
14.8k32553
$endgroup$
add a comment |
$begingroup$
Use Replace with level spec All rather than ReplaceAll:
Replace[<|a -> {c, d, e}|>, d -> Nothing, All]
<|a -> {c, e}|>
Related: Is there a difference between Replace with parameter "All" and ReplaceAll
answered 2 days ago
CoolwaterCoolwater
14.8k32553
$endgroup$
add a comment |
$begingroup$
Use Replace with level spec All rather than ReplaceAll:
Replace[<|a -> {c, d, e}|>, d -> Nothing, All]
<|a -> {c, e}|>
Related: Is there a difference between Replace with parameter "All" and ReplaceAll
answered 2 days ago
CoolwaterCoolwater
14.8k32553
$endgroup$
Use Replace with level spec All rather than ReplaceAll:
Replace[<|a -> {c, d, e}|>, d -> Nothing, All]
<|a -> {c, e}|>
Related: Is there a difference between Replace with parameter "All" and ReplaceAll
answered 2 days ago
CoolwaterCoolwater
14.8k32553
answered 2 days ago
CoolwaterCoolwater
14.8k32553
answered 2 days ago
CoolwaterCoolwater
14.8k32553
answered 2 days ago
CoolwaterCoolwater
14.8k32553
14.8k32553
add a comment |
add a comment |
$begingroup$
Pattern matching to a function evaluation inside an Association answers your question about bug vs expected result.
This will not do what your input suggests but let me anticipate your needs:
<|a -> {b, c, d}, e :> {d, Print[1], d}, f -> d|> //.
{a___, d, b___} :> {a, b} /. (*this way Print is not evaluated*)
d -> Nothing
<|a -> {b, c}, e :> {Print[1]}, f -> Nothing|>
answered 2 days ago
Kuba♦Kuba
104k12201520
$endgroup$
add a comment |
$begingroup$
Pattern matching to a function evaluation inside an Association answers your question about bug vs expected result.
This will not do what your input suggests but let me anticipate your needs:
<|a -> {b, c, d}, e :> {d, Print[1], d}, f -> d|> //.
{a___, d, b___} :> {a, b} /. (*this way Print is not evaluated*)
d -> Nothing
<|a -> {b, c}, e :> {Print[1]}, f -> Nothing|>
answered 2 days ago
Kuba♦Kuba
104k12201520
$endgroup$
add a comment |
$begingroup$
Pattern matching to a function evaluation inside an Association answers your question about bug vs expected result.
This will not do what your input suggests but let me anticipate your needs:
<|a -> {b, c, d}, e :> {d, Print[1], d}, f -> d|> //.
{a___, d, b___} :> {a, b} /. (*this way Print is not evaluated*)
d -> Nothing
<|a -> {b, c}, e :> {Print[1]}, f -> Nothing|>
answered 2 days ago
Kuba♦Kuba
104k12201520
$endgroup$
Pattern matching to a function evaluation inside an Association answers your question about bug vs expected result.
This will not do what your input suggests but let me anticipate your needs:
<|a -> {b, c, d}, e :> {d, Print[1], d}, f -> d|> //.
{a___, d, b___} :> {a, b} /. (*this way Print is not evaluated*)
d -> Nothing
<|a -> {b, c}, e :> {Print[1]}, f -> Nothing|>
answered 2 days ago
Kuba♦Kuba
104k12201520
answered 2 days ago
Kuba♦Kuba
104k12201520
answered 2 days ago
Kuba♦Kuba
104k12201520
answered 2 days ago
Kuba♦Kuba
104k12201520
104k12201520
add a comment |
add a comment |
$begingroup$
For completeness sakes (I believe Coolwater's answer is best):
assoc = Association[ a → {c,d,e} ];
Query
assoc // Query[ All, ReplaceAll[ d → Nothing ] ]
(* <|a -> {c, e}|> *)
Note: This will need repeated use of All for nested associations.
DeleteCases
Before there was Nothing there was DeleteCases and the like:
assoc // DeleteCases[ #, d, Infinity ]&
(* <|a -> {c, e}|> *)
answered 2 days ago
gwrgwr
7,73822558
$endgroup$
add a comment |
$begingroup$
For completeness sakes (I believe Coolwater's answer is best):
assoc = Association[ a → {c,d,e} ];
Query
assoc // Query[ All, ReplaceAll[ d → Nothing ] ]
(* <|a -> {c, e}|> *)
Note: This will need repeated use of All for nested associations.
DeleteCases
Before there was Nothing there was DeleteCases and the like:
assoc // DeleteCases[ #, d, Infinity ]&
(* <|a -> {c, e}|> *)
answered 2 days ago
gwrgwr
7,73822558
$endgroup$
add a comment |
$begingroup$
For completeness sakes (I believe Coolwater's answer is best):
assoc = Association[ a → {c,d,e} ];
Query
assoc // Query[ All, ReplaceAll[ d → Nothing ] ]
(* <|a -> {c, e}|> *)
Note: This will need repeated use of All for nested associations.
DeleteCases
Before there was Nothing there was DeleteCases and the like:
assoc // DeleteCases[ #, d, Infinity ]&
(* <|a -> {c, e}|> *)
answered 2 days ago
gwrgwr
7,73822558
$endgroup$
For completeness sakes (I believe Coolwater's answer is best):
assoc = Association[ a → {c,d,e} ];
Query
assoc // Query[ All, ReplaceAll[ d → Nothing ] ]
(* <|a -> {c, e}|> *)
Note: This will need repeated use of All for nested associations.
DeleteCases
Before there was Nothing there was DeleteCases and the like:
assoc // DeleteCases[ #, d, Infinity ]&
(* <|a -> {c, e}|> *)
answered 2 days ago
gwrgwr
7,73822558
edited 2 days ago
answered 2 days ago
gwrgwr
7,73822558
answered 2 days ago
gwrgwr
7,73822558
answered 2 days ago
gwrgwr
7,73822558
7,73822558
add a comment |
add a comment |
$begingroup$
You may use Query to evaluate the result of the replace in an Association. Query gives direct access to the key's value which then evaluated in Query.
Query[All, # /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
Hope this helps.
answered 2 days ago
EdmundEdmund
26.2k330100
$endgroup$
add a comment |
$begingroup$
You may use Query to evaluate the result of the replace in an Association. Query gives direct access to the key's value which then evaluated in Query.
Query[All, # /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
Hope this helps.
answered 2 days ago
EdmundEdmund
26.2k330100
$endgroup$
add a comment |
$begingroup$
You may use Query to evaluate the result of the replace in an Association. Query gives direct access to the key's value which then evaluated in Query.
Query[All, # /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
Hope this helps.
answered 2 days ago
EdmundEdmund
26.2k330100
$endgroup$
You may use Query to evaluate the result of the replace in an Association. Query gives direct access to the key's value which then evaluated in Query.
Query[All, # /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
Hope this helps.
answered 2 days ago
EdmundEdmund
26.2k330100
answered 2 days ago
EdmundEdmund
26.2k330100
answered 2 days ago
EdmundEdmund
26.2k330100
answered 2 days ago
EdmundEdmund
26.2k330100
26.2k330100
add a comment |
add a comment |
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$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
2 days ago