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
$endgroup$
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
$endgroup$
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
yesterday
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
$endgroup$
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 yesterday
darmualdarmual
413
413
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
yesterday
add a comment |
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
yesterday
1
1
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
yesterday
$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
yesterday
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:
Association
isHoldAllComplete
. 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 Nothing
s:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
$endgroup$
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
$endgroup$
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|>
$endgroup$
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}|> *)
$endgroup$
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.
$endgroup$
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:
Association
isHoldAllComplete
. 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 Nothing
s:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
$endgroup$
add a comment |
$begingroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
Association
isHoldAllComplete
. 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 Nothing
s:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
$endgroup$
add a comment |
$begingroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
Association
isHoldAllComplete
. 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 Nothing
s:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
$endgroup$
The observed puzzle is resolved by the following two observations:
From Leonid's answer in the linked q/a:
Association
isHoldAllComplete
. 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 Nothing
s:
ReplaceAll[d -> Nothing] /@ assoc (* or *)
Map[# /. d -> Nothing &]@<|a -> {c, d, e}|>
<|a -> {c, e}|>
edited yesterday
answered yesterday
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
$endgroup$
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
$endgroup$
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
$endgroup$
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 yesterday
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|>
$endgroup$
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|>
$endgroup$
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|>
$endgroup$
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 yesterday
Kuba♦Kuba
104k12201519
104k12201519
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}|> *)
$endgroup$
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}|> *)
$endgroup$
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}|> *)
$endgroup$
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}|> *)
edited yesterday
answered yesterday
gwrgwr
7,70322558
7,70322558
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.
$endgroup$
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.
$endgroup$
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.
$endgroup$
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 yesterday
EdmundEdmund
26.1k330100
26.1k330100
add a comment |
add a comment |
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$begingroup$
closely related: Pattern matching to a function evaluation inside an Association
$endgroup$
– kglr
yesterday