Two arrays, same length. If first array values equals true get values from second array

Question

I have two arrays. They are always the same length. If userEmotions[index] value is true I need to add userTimeData[index] value to a variable:

var userEmotions = [false, true, false, true],
    userTimeData = [140, 320, 730, 50],
    userPercentage = 0;

// e.g add 320 and 50 to userPercentage:
// userPercentage == 370

How do I go about achieving this?

do you need just a single value or an array of values? what have you tried? — Nina Scholz
– Nina Scholz, Commented Feb 14, 2018 at 14:53
"How do I go about achieving this?" -- you take the third sentence from the text and turn it into code. As simple as: for (index in userEmotions) { if (userEmotions[index]) { userPercentage += userTimeData[index]; } }. Not enough to compute a percentage, but you can use it as a starting point. — axiac
– axiac, Commented Feb 14, 2018 at 14:54
userPercentage = userEmotions.reduce((sum, e, i) => sum + (e && userTimeData[i]), 0) — Aikon Mogwai
– Aikon Mogwai, Commented Feb 14, 2018 at 14:56

Nina Scholz · Accepted Answer · 2018-02-14 15:15:18Z

2

You could use Array#indexOf for the first single value or zero as default value.

var userEmotions = [false, true, true],
    userTimeData = [140, 320, 730],
    userPercentage = userTimeData[userEmotions.indexOf(true)] || 0;

console.log(userPercentage);

For getting an array of values, you could filter the values.

var userEmotions = [false, true, true],
    userTimeData = [140, 320, 730],
    userPercentages = userTimeData.filter((_, i) => userEmotions[i]);

console.log(userPercentages);

edited Feb 14, 2018 at 15:15

answered Feb 14, 2018 at 14:57

Nina Scholz

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5 Comments

Buh Buh Over a year ago

Oh, I was just demonstrating that your code doesn't give the correct answer when the number of trues is not one.

Nina Scholz Over a year ago

@BuhBuh, the user wants to get a single value, and the first true value's index should be taken for the result, as the title of the post asks. what goes wrong with another true in the userEmotions array?

Buh Buh Over a year ago

I see now you have interpenetrated the question differently. I understood first to refer to the first array, where you took it to mean first boolean. Maybe you are right. The question is ambiguous.

Laniakea Over a year ago

Now that I read the question again, yes it is ambiguous and I meant first array. userPercentages.reduce((a, b) => a + b, 0). Out of curiosity what does the (_, part in filter() do?

Nina Scholz Over a year ago

_ is just a variable, which is not used.

Pete · Accepted Answer · 2018-02-14 14:55:59Z

2

You can use a for loop:

var userEmotions = [false, true, false],
  userTimeData = [140, 320, 730],
  userPercentage = 0;

for (i = 0; i < userEmotions.length; i++) { //loop the length of the array
  if (userEmotions[i]) { // check userEmotions is true
    userPercentage += userTimeData[i]; // if it is add userTimeData to percentage
  }
}

console.log(userPercentage);

answered Feb 14, 2018 at 14:55

Pete

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Comments

Buh Buh · Accepted Answer · 2018-02-14 15:19:58Z

1

The OP wanted alternative approaches, so:

userEmotions = [false, true, false],
userTimeData = [140, 320, 730],
userPercentage = userEmotions
    .map(x => x ? 1 : 0)
    .map((x, i) => x * userTimeData[i])
    .reduce((a,b) => a+b);

console.log(userPercentage);

answered Feb 14, 2018 at 15:19

Buh Buh

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Comments

Rishikesh Dhokare · Accepted Answer · 2018-02-14 14:56:19Z

0

Why over engineer it, a simple for loop solves your problem -

var userEmotions = [false, true, false],
    userTimeData = [140, 320, 730],
    userPercentage = 0;

for (i = 0; i < userEmotions.length; i++) {
  if (userEmotions[i]) {
    userPercentage += userTimeData[i];
  }
}

console.log(userPercentage);

answered Feb 14, 2018 at 14:56

Rishikesh Dhokare

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Comments

user9099485 · Accepted Answer · 2018-02-14 14:58:19Z

0

can you try this :

for(let i = 0 ; i < userEmotions .length ; i++){
   if(userEmotions[i]){
       userPercentage = userTimeData[i]
   }
}

Let me know if it help you :)

answered Feb 14, 2018 at 14:58

user9099485

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