WolframLang: Association, Misc
xtodo work in progress
Functions that Map to Values
Functions that work on lists, when used on association, they apply to the values. (keys are ignored)
e.g.
Take,
Select,
[see WolframLang: Association: Filter]
Functions that Apply to Keys
- KeySort, KeySortBy — sort an association by its keys
- KeyMap — map a function over the keys in an association
- KeyValueMap — map a function over keys and values in an association
Functions Operating on Lists of Associations
Merge[{assoc1,assoc2 etc}, f]-
merges associations, applying function f to combine values with the same key. WARNING: f is applied to all keys, even unique keys.
f should be a function that takes one argument of List . (the number of items in the list is one to the count of associations). Item of the list is either a value of a single unique key, or values of the same key.
Mergexx = Association[ a -> 1, b -> 2 ]; yy = Association[ a -> 10, c -> 3 ]; (* merge. showing how the f works. note that f is applied to all key's values *) Merge[ {xx, yy}, f ] === <|a -> f[{1, 10}], b -> f[{2}], c -> f[{3}]|>
xx = Association[ a -> 1, b -> 2 ]; yy = Association[ a -> 10, c -> 3 ]; (* merge. combine values to list *) Merge[ {xx, yy}, List ] === <|a -> {{1, 10}}, b -> {{2}}, c -> {{3}}|>
xx = Association[ a -> 1, b -> 2 ]; yy = Association[ a -> 10, c -> 3 ]; (* merge. new key's value is the total their values *) Merge[ {xx, yy}, Total ] === <|a -> 11, b -> 2, c -> 3|>
Merge[{key1 -> val1, key2 -> val2 etc}, f]- merge a List of Rules .
- Catenate — catenate elements from multiple associations
- JoinAcross — do the analog of a database join on multiple associations
- Dataset — representation supporting general structured data queries
- Key — indicate a key within a part specification
- #name — a slot in a pure function that picks out value with key "name" in an association
- AssociationQ — test if an expression is a valid association
Elements of Associations
Pattern Matching with Associations
- KeyValuePattern — elements that can appear anywhere in an association
Functions That Create Associations
- Association — turn a list of rules into an association
- AssociationMap — create an association by applying a function to a list of keys
- AssociationThread — create an association from a list of keys and a list of values
- Counts, CountsBy — associate values with the number of times they occur
- PositionIndex — build an index of positions at which values occur
GroupBy
