WolframLang: Association, Add Key

By Xah Lee. Date: . Last updated: .

Add One Key/Val Pair by Assignment Syntax

Tip: by WolframLang naming convention, function whose name ends in “To” or “From” modifies a variable.

assocVar[key]=val
Add a key value pair to assocVar. If the key exist, value is updated. assocVar must be a variable.

Append Key/Value and Modify Variable

AssociateTo[ assocVar, rule ]
  • Add a entry to a assoc variable and modify the variable. Return the updated value.
  • If the key exist, value is updated.
AssociateTo
xx = Association[ a -> 3 ];
AssociateTo[ xx, {c -> 4} ];

xx === <|a -> 3, c -> 4|>
AssociateTo[ assocVar, {rule1, rule2 etc} ]
Add multiple entries.
xx = Association[ a -> 3 ];
AssociateTo[ xx, {c -> 4, m -> 9} ];
xx === <|a -> 3, c -> 4, m -> 9|>

AppendTo

AppendTo is usually for working with List, but it works with Association too. It works the same way as AssociateTo.

AppendTo[ assocVar, rule ]
Append one or more entries to a assoc variable. Use list for more than one.
If the key exist, value is updated.
AppendTo
xx = Association[ a -> 3, b -> 2 ];
AppendTo[ xx, {b -> 4, m -> 1} ];
xx == <|a -> 3, b -> 4, m -> 1|>
(* AppendTo works the same way as AssociateTo *)

xx = Association[ a -> 3 ];
AppendTo[ xx, b -> 4 ];

yy = Association[ a -> 3 ];
AssociateTo[ yy, b -> 4 ];

xx === yy

WolframLang: Association (Key Value Pairs)

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