WolframLang: Association (Key Value Pairs)
WolframLang's Association is a dedicated structure for list of key/value pairs. Similar to Lisp Association List, JavaScript Map, Python Dictionary, Perl Hash Table. It provides a efficient implementation of ordered list of pairs, when you have large number of pairs such as over a hundred pairs.
Create Association
Association[rule1, rule2 etc]
-
(short syntax:
<|args|>
is same asAssociation[args]
)Association is an ordered list of key/value pairs.
Each rule is a pair of values in one of the form
Rule[expr1, expr2]
(short syntaxexpr1 -> expr2
)RuleDelayed[expr1, expr2]
(short syntaxexpr1 :> expr2
)
The left-hand-side is the key. The right-hand-side is the value. [see WolframLang: Rule]
- The key or value can be any expression.
- The key is usually a Symbol or a string.
- If key are duplicated, the earlier ones are removed.
(* create a key/value pairs list *) xx = Association[ a -> 3, b -> 2 ] (* short syntax *) yy = <| a -> 3, b -> 2 |> xx === yy
Association[{args}]
-
same as
Association[args]
Count/Length
Length[ assoc ]
- return number of pairs.
Length