map-reduce ( ..a seq map-quot: ( ..a elt -- ..b intermediate ) reduce-quot: ( ..b prev intermediate -- ..a next ) -- ..a result )
Factor handbook » The language » Collections » Sequence operations » Sequence combinators

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Vocabulary
sequences

Inputs

seq	a sequence
map-quot	a quotation with stack effect ( ..a elt -- ..b intermediate )
reduce-quot	a quotation with stack effect ( ..b prev intermediate -- ..a next )

Outputs

result

an object

Word description
Calls map-quot on each element and combines the results using reduce-quot in the same manner as reduce, except that there is no identity element, and the sequence must have a length of at least 1.

Errors
Throws an error if the sequence is empty.

Examples

USING: sequences prettyprint math ; { 1 3 5 } [ sq ] [ + ] map-reduce .
35

Definition

USING: kernel ;

IN: sequences

: map-reduce
    ( ..a seq map-quot: ( ..a elt -- ..b intermediate ) reduce-quot: ( ..b prev intermediate -- ..a next ) -- ..a result )
    [ [ [ first ] keep ] dip [ dip ] keep ] dip compose
    1 each-from ; inline