Observable array inside array, digit sum?

Question

I have an array which may have nested arrays. I want to sum all numbers inside the parent no matter how many 'child' arrays are there.

Why doesn't it work this way. The else is complaining about acc1 being an array, which is normal but still, what's the problem with this approach?

Observable.from([1, 2, 3, [ 1, 2, 3, 4]])
    .map(x => x)
    .reduce((acc1, y) => {
      if (Array.isArray(y)) {
        return (y.reduce((acc2, x) => acc2 + x));
      } else {
        return acc1 + y;
      }
    })
    .subscribe(res => console.log(res))

Result should be 16

Boris Lobanov · Accepted Answer · 2018-03-01 22:00:27Z

2

You were very close:

Observable.from([1, 2, 3, [ 1, 2, 3, 4]])
    .map(x => x)
    .reduce((acc1, y) => {
      if (Array.isArray(y)) {
        return acc1 + (y.reduce((acc2, x) => acc2 + x)); // just add acc1 to your reduced array
      } else {
        return acc1 + y;
      }
    })
    .subscribe(res => console.log(res))

answered Mar 1, 2018 at 22:00

Boris Lobanov

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2 Comments

maxime1992 Over a year ago

Two things to notice here: 1) the .map(x => x) is useless, taking a value and returning the same value does not make sense. 2) If you want to have update of the result not only at the end but for every value passing down the stream, instead of using reduce (the one on observable), you could use scan :)

EugenSunic Over a year ago

I know it is. But I have to have an array in order to apply reduce. If I don't have map then reduce can not be applied directly on a observable array.

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