How to use reduce to return an object in Javascript?

Question

I'm trying to count the number of odd and even numbers in an array by using the Array.reduce() method. When I run the below code, I get the error "odd is not defined." How/where do I define odd to get this code to work?

var numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];
var oddEvenCounts = numbers.reduce(function(counts, number) {
   if (number % 2 === 1) {
     counts[odd]++
   } else {
     counts[even]++;
   }
   return counts;
 }, {});

use counts.odd and counts.even instead of counts[....] or even counts["odd"] and counts["even"] — Titus
– Titus, Commented Sep 25, 2017 at 3:06

dork · Accepted Answer · 2017-09-25 03:11:13Z

9

Well, odd isn't defined. What you should do is either put odd/even in quotes (counts['odd']) or use dot notation (counts.odd).

Also, since odd and even aren't defined, incrementing them would result into NaN. The initial value should instead be { odd: 0, even: 0 }.

var numbers = [5, 3, 8, 6, 9, 1, 0, 2, 2];
var oddEvenCounts = numbers.reduce(function(counts, number) {
   if (number % 2 === 1) {
     counts['odd']++;
   } else {
     counts['even']++;
   }
   return counts;
 }, { odd: 0, even: 0 });
 
 console.log(oddEvenCounts);

answered Sep 25, 2017 at 3:11

dork

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Comments

yaas · Accepted Answer · 2019-05-30 22:06:31Z

1

This is a function that can do it for you.

function oddEvenCounts(arr) {
  const counts = {
    even: 0,
    odd: 0
  };
  arr.forEach(n => {
    if(n % 2 === 0) {
      counts.even++;
    } else {
      counts.odd++
    }
  });
  return counts;
}

const array = [5, 3, 8, 6, 9, 1, 0, 2, 2];
console.log(oddEvenCounts(array));

answered May 30, 2019 at 22:06

yaas

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Comments

Terry · Accepted Answer · 2022-02-19 23:00:10Z

0

Answer using ES6+

const sumEvenOdd = (numbersArray) => {
    return numbersArray.reduce((acc, current) => current % 2 === 0 ? {...acc,'even':acc['even'] + current} : {...acc, 'odd':acc['odd'] + current}, {"even":0, "odd":0})
}'

console.log(sumEvenOdd([1, 6, 8, 5, 3]));
// Expected results: {even: 14, odd: 9}

edited Feb 19, 2022 at 23:00

Terry

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answered Feb 15, 2022 at 4:06

Rajat Gupta

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1 Comment

klutt Over a year ago

Please format your code with code blocks

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