collect-by ( ... seq quot: ( ... obj -- ... key ) -- ... assoc )

Vocabulary
assocs

Inputs

seq	a sequence
quot	a quotation with stack effect ( ... obj -- ... key )

Outputs

assoc

an assoc

Word description
Applies a quotation to each element in the input sequence and returns a hashtable of like elements. The keys of this hashtable are the output of quot and the values at each key are the elements that transformed to that key.

Examples
Collect even and odd elements:

USING: assocs math prettyprint ; { 11 12 13 14 14 13 12 11 } [ odd? ] collect-by .
H{ { t V{ 11 13 13 11 } } { f V{ 12 14 14 12 } } }

Collect strings by length:

USING: assocs prettyprint sequences ; { "one" "two" "three" "four" "five" } [ length ] collect-by .
H{ { 3 V{ "one" "two" } } { 4 V{ "four" "five" } } { 5 V{ "three" } } }