Question: take items from stream while value is less than a max value

[bapti]

Hi, I've got a quick quesiton about how to take items from an infinite stream - I'd like to be able to do something like below.

_(infiniteNumberGenerator)
  .takeWhile( (count) => {
    return count < max;
  })
  .map(...)

Is this supported with the methods or would I have to implement something? Take does this by using slice. I could estimate how many i need using some maths but I thought it would be nice just to have a clause that stops the stream after enough has been pulled. Is this doable?

Thanks
Neil

[bapti]

Sorry, figured it out

var takeWhile = function (f) {
  return (err, x, push, next) => {
    if (err) {
      // pass errors along the stream and consume next value
      push(err);
      next();
    }
    else if (x === _.nil) {
      // pass nil (end event) along the stream
      push(null, x);
    }
    else {
      // pass on the value only if the value passes the predicate
      if (f(x)) {
        push(null, x);
        next();
      } else {
        push(null, _.nil)
      }
    }
  }
}

paired with

.consume(takeWhile((x) => {
      return x < max
    }))

[LewisJEllis]

Glad you worked this out, and with pure highland you're spot on what you're looking for. One note to be aware of - transducer support was added in #223 and takeWhile is available as a transducer (see also https://github.com/cognitect-labs/transducers-js), so you can use that to avoid writing your own takeWhile implementation if you so prefer.

[bapti]

@LewisJEllis - is this something that you'd like as a pull request for highland? Happy to add it with tests.

[LewisJEllis]

Probably not now, but almost definitely after 3.0 and the module system. We try to keep the core lib from becoming a 'kitchen sink', but takeWhile could easily fit in a module after 3.0. For now, we access the kitchen sink via transducers.

[bapti]

@LewisJEllis thanks for that, is there a ballpark for the 3.0 release?

[apaleslimghost]

Soon™ 😉

Not committing to anything here, but possibly some time in the next 6 months? We're tracking progress over at #179, although we've not made much progress for the last couple of months.

[mauriciocap]

PR with takeWhile #677 , thanks!