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KeyValuePattern

Status: Stable

documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

Description

KeyValuePattern[{k1 -> p1, ...}]
    A pattern matching an association (or
    list of rules) that contains keys matching k1, ... with values matching
    p1, .... Value patterns may bind (e.g. KeyValuePattern[{"a" -> v_}]).
    KeyValuePattern[k -> p] is the single-key form.

Examples

All examples below are verified against the current Mathilda build.

In[1]:= MatchQ[<|"a" -> 1, "b" -> 2|>, KeyValuePattern[{"a" -> _}]]
Out[1]= True

In[2]:= Replace[<|"a" -> 5, "b" -> 2|>, KeyValuePattern[{"a" -> v_}] :> v]
Out[2]= 5

In[3]:= Cases[{<|"t" -> 1|>, <|"t" -> 2|>, <|"x" -> 3|>}, KeyValuePattern[{"t" -> _}]]
Out[3]= {<|"t" -> 1|>, <|"t" -> 2|>}

In[1]:= Cases[{<|"p" -> 3|>, <|"p" -> 9|>}, KeyValuePattern[{"p" -> v_}] /; v > 5 :> v]
Out[1]= {9}

In[1]:= area[KeyValuePattern[{"w" -> w_, "h" -> h_}]] := w h; area[<|"w" -> 3, "h" -> 4|>]
Out[1]= 12

Implementation notes

Attributes: Protected.

Implementation status

Stable — documented, exercised by the test suite and/or worked examples, with no known limitations recorded.

References