Pattern Matching with Associations
Version 11 introduces several functions to simplify the manipulation and pattern matching of associations.
Use KeyMemberQ and KeyFreeQ to test whether or not a key is part of an association.
In[1]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_72.png)
KeyMemberQ[<|a -> 1, b -> 2, c -> 3|>, a]
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![](assets.en/pattern-matching-with-associations/O_75.png)
In[2]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_73.png)
KeyFreeQ[<|a -> 1, b -> 2, c -> 3|>, a]
Out[2]=
![](assets.en/pattern-matching-with-associations/O_76.png)
KeyValuePattern allows you to match a complete association that contains one or more given rules.
In[3]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_74.png)
MatchQ[<|a -> 1, b -> 2, c -> 3|>, KeyValuePattern[b -> _]]
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![](assets.en/pattern-matching-with-associations/O_77.png)
In[4]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_75.png)
MatchQ[<|a -> 1, b -> 2, c -> 3|>, KeyValuePattern[{c -> _, a -> _}]]
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![](assets.en/pattern-matching-with-associations/O_78.png)
Compute data on the gravitational field at several points of the Earth.
In[5]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_76.png)
points = {{40, -100, 691}, {30, -120, 560}, {80, 70, 91}};
data = GeogravityModelData /@ points
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![](assets.en/pattern-matching-with-associations/O_79.png)
Select the cases for which the field magnitude is larger than the standard average value.
In[6]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_77.png)
Cases[data,
KeyValuePattern[
"Magnitude" -> _?(GreaterThan[
Quantity[1, "StandardAccelerationOfGravity"]])]]
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![](assets.en/pattern-matching-with-associations/O_80.png)
Use KeyValueMap to further process each key-value pair.
In[7]:=
![Click for copyable input](assets.en/pattern-matching-with-associations/In_78.png)
Cases[data,
KeyValuePattern[
"Magnitude" -> _?(GreaterThan[
Quantity[1, "StandardAccelerationOfGravity"]])]];
KeyValueMap[
EntityProperty["GeogravityModel", #1] ->
UnitConvert[#2, "Imperial"] &, First[%]]
Out[7]=
![](assets.en/pattern-matching-with-associations/O_81.png)