Compare two arrays of numbers and return array of highest values

Question

What would be the most efficient way to compare two arrays of integers and return a unique array of the higher corresponding integers in each array?

(can use lodash)

ex:

var arr1 = [0, 1, 2, 1, 0];
var arr2 = [1, 0, 0, 3, 0];

// result = [1, 1, 2, 3, 0];

Why are you worried about efficiency before you have figured out how to do it in the first place? What do you mean by a "unique" array? What if the arrays are of different length? — user663031
– user663031, Commented Sep 18, 2015 at 16:28
Are you sure your sample code shows the correct result? "return a unique array" - You mean an array of unique values? — Adrian Lynch
– Adrian Lynch, Commented Sep 18, 2015 at 16:30
Ah, I think I understand now. Compare the value at the same index and return the higher of the two. — Adrian Lynch
– Adrian Lynch, Commented Sep 18, 2015 at 16:34

Adrian Lynch · Accepted Answer · 2015-09-18 16:35:47Z

3

Here's my first, less efficient method:

var arr1 = [0, 1, 2, 1, 0];
var arr2 = [1, 0, 0, 3, 0];

arr1.map(function (item, i) {
  return Math.max(item, arr2[i])
}); // [1, 1, 2, 3, 0]

What it lacks in speed, it gains in beauty!

Or for you ES6 boverers:

var arr1 = [0, 1, 2, 1, 0];
var arr2 = [1, 0, 0, 3, 0];

arr1.map((item, i) => Math.max(item, arr2[i])); // [1, 1, 2, 3, 0]

answered Sep 18, 2015 at 16:35

Adrian Lynch

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1 Comment

Jamie Kudla Over a year ago

Doncha mean const for the latter :p

0x860111 · Accepted Answer · 2015-09-18 16:53:28Z

2

function selectHighestValues (arr1, arr2) {
  var maxLength = Math.max(arr1.length, arr2.length);
  var _arr = [];
  for (var i = 0; i < maxLength; i++) {
    if (arr1[i] && arr2[i]) {
      _arr[i] = Math.max(arr1[i], arr2[i]);
    } else if (arr1[i]) {
      _arr[i] = arr1[i]; 
    } else {
      _arr[i] = arr2[i]; 
    }

  }
  return _arr;
}

With splicing longest array and concatenation:

function selectHighestValues (arr1, arr2) {
  var minLength = Math.min(arr1.length, arr2.length);
  var maxLength = Math.max(arr1.length, arr2.length);
  var longestArrayIndex = arr1.length > arr2.length ? 0 : 1;
  var _arr = [];
  for (var i = 0; i < minLength; i++) {
    _arr[i] = Math.max(arr1[i], arr2[i]);
  }
  if (maxLength > minLength) {
    var sliced = Array.prototype.slice.call(arguments[longestArrayIndex], minLength, maxLength);
    _arr = Array.prototype.concat.call(_arr, sliced);
  }
  return _arr;
}

edited Sep 18, 2015 at 16:53

answered Sep 18, 2015 at 16:30

0x860111

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3 Comments

devlin carnate Over a year ago

Won't you get an undefined offset using maxLength if one array is shorter than the other?

0x860111 Over a year ago

Fixed. If one array shorter then other, function will just copy values from longest array.

0x860111 Over a year ago

Added new method with splicing longest array and concatenation.

house9 · Accepted Answer · 2015-09-18 16:30:19Z

1

Brute force!

var arr1 = [0, 1, 2, 1, 0];
var arr2 = [1, 0, 0, 3, 0];
var result = [];

for(var i = 0; i < arr1.length; i++) {
  if (arr1[i] > arr2[i]) {
    result.push(arr1[i]);  
  } else {
    result.push(arr2[i]);
  }
}

answered Sep 18, 2015 at 16:30

house9

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1 Comment

user663031 Over a year ago

Phooey, I was hoping for a recursive, functional solution.

Dan O · Accepted Answer · 2015-09-18 16:38:21Z

1

_.zipWith(arr1, arr2, function(el1, el2) {
    return (el1 > el2 ? el1 : el2);
});

_.zipWith() is only in lodash 3.x I believe.

answered Sep 18, 2015 at 16:38

Dan O

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Comments

Adam Boduch · Accepted Answer · 2015-09-19 14:22:54Z

0

Using zip(), map(), and max():

_.map(_.zip(arr1, arr2), _.ary(_.max, 1));

answered Sep 19, 2015 at 14:22

Adam Boduch

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