I think you can use group-by from sequences.extras. It works similar
to map-runs:
{ 1 5 "hello" 2 "world" 3 6 9 "!" } [ integer? ] group-by [ swap [ sum
] [ first ] if ] { } assoc>map .
{ 6 "hello" 2 "world" 18 "!" }
2016-12-16 11:16 GMT+01:00 Alexander Ilin <ajs...@yandex.ru>:
> Hello!
>
> I was solving this issue, and it got me wondering if there is a better
> solution somewhere in the library. Could you check this out?
>
> I want to find consecutive runs of numbers and replace them with a sum,
> while preserving all other objects in the sequence (currently only strings
> are in there). For example:
>
> IN: { 1 5 "hello" 2 "world" 3 6 9 "!" } collapse-numbers
> OUT: { 6 "hello" 2 "world" 18 "!" }
>
> Here's the `collapse-numbers` implementation that I came up with:
>
> :: collapse-numbers ( seq -- seq' )
> f :> accum! seq [
> accum 2dup [ number? ] both? [
> + accum! f
> ] [
> swap accum!
> ] if
> ] map sift accum suffix ;
>
> Using a local variable for a side-effect in map feels like cheating,
> straight from my imperative programming background.
> Is there a way to, maybe, convert numbers into subsequences?
>
> IN: { 1 5 "hello" 2 "world" 3 6 9 "!" } [ number? ] map-runs
> OUT: { { 1 5 } "hello" { 2 } "world" { 3 6 9 } "!" }
>
> If we had something like `map-runs`, the whole task could be solved in a
> more functional way:
>
> : collapse-numbers ( seq -- seq' )
> [ number? ] map-runs [ dup string? [ sum ] unless ] map ;
>
> What are your thoughts on this? Do we **have** something like `map-runs`?
> Do we **need** it? Should I have used PEGs to parse the sequence?
>
> ---=====---
> Александр
>
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--
mvh/best regards Björn Lindqvist
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