Javascript: Check if all elements of an array are the same as a variable, or none of them are

Question

I have a javascript variable that is an array of arrays. Then I have a variable below it. Like this:

var cars = [
    ["ford mustang",1955,"red"],
    ["dodge dart",1963,"green"],
    ["pontiac",2002,"green"],
]

var colour = "blue";

Now I need to check for if either the third values of each array are all the same as the variable, colour, or they are all different. If one of those conditions are true, I want to execute some other code. So in the above example, the condition would be true because none of the values are "blue". It would also be true if they were all "blue".

Hopefully I've made myself clear.

I can think of a number of ways to do this. You can count the number of matches, and see if it's 0 or cars.length. You can loop over the elements. After you find a match, then stop if you find a mismatch and report failure; after you find a mismatch, stop if you find a match. — Barmar
– Barmar, Commented Nov 12, 2013 at 1:21
You've already described the algorithm you need; take the next step and try to code it yourself. — musical_coder
– musical_coder, Commented Nov 12, 2013 at 1:22

Downgoat · Accepted Answer · 2015-07-23 21:50:14Z

9

There are two functions in JavaScript just for that:

allCarsAreRed = cars.every(function(car) { return car[2] == 'red' })
atLeastOneCarIsRed = cars.some(function(car) { return car[2] == 'red' })
noRedCars = cars.every(function(car) { return car[2] != 'red' })

edited Jul 23, 2015 at 21:50

Downgoat

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answered Nov 12, 2013 at 1:27

georg

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3 Comments

jfriend00 Over a year ago

These do work nicely, but they don't work in IE8 or earlier so one would need a shim for them if you need to support IE8.

georg Over a year ago

@jfriend00: yes, every time you mention a ES5 feature in a post, someone comes up with this IE8 comment. To be honest, I find these comments rather misleading. First, no one "needs" to support IE8, quite the contrary - the less we support it, the sooner it dies - to everyone's benefit. Second, and worse, these comments scare beginners away from modern javascript and promote outdated programming practices.

jfriend00 Over a year ago

@thg435 - You don't get to decide whether someone needs to support IE8 or not. That is their decision. I just added some more info to your answer that might be useful if someone had a requirement to support IE8. Why does that additional info both you. I didn't downvote you - just added more info.

DavidC · Accepted Answer · 2013-12-04 20:19:47Z

5

var colour = 'blue'
var all = true;
var none = true;
for (var i = 0; i < cars.length; i++) {
   if (cars[i][2] !== colour) {
      all = false;
   } else  {
      none = false;
   }

}

edited Dec 4, 2013 at 20:19

answered Nov 12, 2013 at 1:23

DavidC

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4 Comments

Barmar Over a year ago

Use else instead of comparing twice.

Barmar Over a year ago

You're still comparing twice. Just use else, not else if.

eshellborn Over a year ago

Thank you! I thought about setting the variables to false and changing them to true, but I couldn't figure out how that would work. This works awesome.

Khamidulla Over a year ago

To @eshellborn, before using this answer just make sure that you obtain length of your array variable just once. Not every time when you iterate.

Khamidulla · Accepted Answer · 2013-11-12 01:36:40Z

3

Do you need something like this?

var cars_length = cars.length;
var all_same = true;
var all_different = true;
for(var i=0; i<cars_length; i++)
{
    if(cars[i].[2] == colour)
    {
       all_same = false;
    }
    else
    {
       all_different = false;
    }
}

if(all_same)
{
   console.log('all same');
}
else
{
   if(all_different)
   {
       console.log('all different');
   }
   else
   {
       console.log('nor all same, nor all different');
   }
}

edited Nov 12, 2013 at 1:36

answered Nov 12, 2013 at 1:21

Khamidulla

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Comments

Vijay Thorat · Accepted Answer · 2016-04-25 17:53:11Z

0

Look at bellow Solution

var arr = ["a", "b", "c", "d"]
var allZero = true;
for (var i = 0; i < arr.length; i++) 
{
    if (arr[i][2] != 0) 
    {
        allZero = false;
        break;
    }
}
if (allZero) 
{
    console.log("ALL are Zero");
}

edited Apr 25, 2016 at 17:53

answered Apr 25, 2016 at 17:10

Vijay Thorat

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1 Comment

Jeff Puckett Over a year ago

this doesn't address the multidimensional aspect of the question

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