split stream into two

[Strider]

Hi. Does flyd has an operation which takes a stream and a predicate, just like filter but returns not one stream, but two: one for values where predicate is true and other for falsy.

var input = flyd.stream()
…
var pred = isEven /* any predicate */
var pair = split(pred, input) /*[0] → «truey», [1] → «falsy» */

var evens = pair[0]
var odds  = pair[1]
/* or use destructurization */

Is this a good idea or I got something conceptually wrong? I can use just two filter's but split is better, since it automatically negate predicate for second stream, so both streams does not have rubbish values from ancestor. Is this acceptable for flyd? Other FRP?

[Simon Friis Vindum]

Hello

I am not sure exactly what you mean that both streams will have rubbish values from their ancestor if you use filter?

[Strider]

@paldepind,

var evens = filter(isEven, input)
var odds  = input // I can't just use input as «else»
// I need to negate predicate:
var odds  = filter(not(isEven), input) 
// split do it for me

[Simon Friis Vindum]

What about:

function split(pred, stream) {
  return [filter(pred, stream), filter(function(v) { return !pred(v); }, stream);
};

[Strider]

@paldepind, yes, I've implemented it in similar manner.