Why Does My Recursive Function Return Undefined?

Question

I don't understand why return weights_data returns undefined, and console.log(weights_data) returns something.

const getWeightReattributeProportionally = (weights_data, weight, z = 0) => {

  weights_data.forEach( (r, i) => weights_data[i] = (r * weight) + r );

  if ( weights_data.reduce( (a, b) => a + b) >= 0.9999999999999999 ) {

    console.log(weights_data);

    return weights_data;

  } else {

    getWeightReattributeProportionally(weights_data, weight *= weight, z += 1);

  }

}

const data = [0.12, 0.22, 0.32, 0.18]

const aaaa = getWeightReattributeProportionally(data, 0.16)

console.log(aaaa)

the condition is never met. it always returns false.

Randy Casburn
– Randy Casburn

2020-10-27 22:34:35 +00:00
Commented Oct 27, 2020 at 22:34 — Randy Casburn
– Randy Casburn, Commented Oct 27, 2020 at 22:34

IvanD · Accepted Answer · 2020-10-27 22:36:37Z

1

You forgot that you need to return the result of the recursive function:

const func = (weights_data, weight, z = 0) => {
  weights_data.forEach((r, i) => weights_data[i] = (r * weight) + r)
  if (weights_data.reduce((a, b) => a + b) >= 0.9999999999999999) {
    console.log(weights_data)
    return weights_data
  } else {
    return func(weights_data, weight *= weight, z += 1) // NEW!
  }
}

const data = [0.12, 0.22, 0.32, 0.18]

const aaaa = func(data, 0.16)

console.log(aaaa)

Also, you have a bug in your code: z is never used anywhere in your function

answered Oct 27, 2020 at 22:36

IvanD

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1 Comment

IvanD Over a year ago

Please upvote and mark my answer as accepted if it helped you :)

Nicholas Carey · Accepted Answer · 2020-10-28 02:15:41Z

0

Unless your recursive function uses side effects (e.g., manipulating global/shared state, writing to a file, etc.) to do its job, every invocation, including the outermost, must return its results to its caller.

If it doesn't, how can the caller know what the recursive call did?

answered Oct 28, 2020 at 2:15

Nicholas Carey

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