Rebol Programming/extract

= USAGE: = EXTRACT series width /index pos /default value /into output

= DESCRIPTION: = Extracts a value from a series at regular intervals.

EXTRACT is a function value. = ARGUMENTS =
 * series -- (Type: series)
 * width -- Size of each entry (the skip) (Type: integer)

= REFINEMENTS =
 * /index -- Extract from an offset position
 * pos -- The position (Type: any)
 * /default -- Use a default value instead of none
 * value -- The value to use (will be called each time if a function) (Type: any)
 * /into -- Insert into a buffer instead (returns position after insert)
 * output -- The buffer series (modified) (Type: series)

= (SPECIAL ATTRIBUTES) =
 * catch

= SOURCE CODE = extract: func [ {Extracts a value from a series at regular intervals.} [catch] series [series!] width [integer!] "Size of each entry (the skip)" /index "Extract from an offset position" pos "The position" [number! logic! block!] /default "Use a default value instead of none" value {The value to use (will be called each time if a function)} /into {Insert into a buffer instead (returns position after insert)} output [series!] "The buffer series (modified)" /local len val ][ if zero? width [return any [output make series 0]] len: either positive? width [ divide length? series width ] [   divide index? series negate width ]  unless index [pos: 1] either block? pos [ if empty? pos [return any [output make series 0]] parse pos [some [number! | logic! | set pos skip (         throw-error 'script 'expect-set reduce number! logic!] type? get/any 'pos]        ) unless into [output: make series len * length? pos] if all [not default any-string? output] [value: copy ""] if binary? series [series: as-string series] forskip series width [forall pos [ if none? set/any 'val pick series pos/1 [set/any 'val value] output: insert/only output get/any 'val ]] ] [    unless into [output: make series len] if all [not default any-string? output] [value: copy ""] if binary? series [series: as-string series] forskip series width [ if none? set/any 'val pick series pos [set/any 'val value] output: insert/only output get/any 'val ] ]   either into [output] [head output] ]