WolframLang: Association, Add Key

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