Create a function to evaluate if all elements in the array are the same

Question

Problem

I'm trying to create a function that evaluates an array and if every element inside the array is the same, it would return true and otherwise false. I don't want it to return true/false for each individual element, just for the entire array.

Attempt 1

This method works, but it returns true/false for each element in the array:

function isUniform(arr){
    let first = arr[0];
    for (let i = 1; i <arr.length; i++){
        if (arr[0] !== arr[i]){
            console.log(false);
        } else {
            console.log(true);
        }
    }
}

Attempt 2

This method returns true/false, once and then prints true again at the end:

function isUniform(arr){
    let first = arr[0];
    for (let i = 1; i <arr.length; i++){
        if (arr[0] !== arr[i]){
            console.log(false);
        }
    }
    console.log(true);
}

Mark · Accepted Answer · 2019-03-23 15:20:16Z

3

If you want to test if something is true for every element of an array, you don't really need to write much — you can use array.every for this and just compare the first element. every() is nice because it will return early if a false condition is found.

var arr1 = [1, 1, 1, 1, 1, 1, 1]
var arr2 = [1, 1, 1, 2, 1, 1, 1]

console.log(arr1.every((n, _, self) => n === self[0]))
console.log(arr2.every((n, _, self) => n === self[0]))

This will return true for an empty array, which may or may not be what you want.

answered Mar 23, 2019 at 15:20

Mark

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5 Comments

Kunal Mukherjee Over a year ago

This is the best answer

Nina Scholz Over a year ago

@KunalMukherjee, this is a different approach, but not an answer to the question.

Kunal Mukherjee Over a year ago

@NinaScholz the OP is asking for if all the elements in the array are the same or not

Ruchi Roy Over a year ago

Thank you! I'll keep this in mind in the future - right now I'm restricted to just using a for loop or for each, but I'm glad I learned this.

Nina Scholz Over a year ago

if only the question is to check, then is clearly a duplicate question and a matter of a close request.

Ele · Accepted Answer · 2019-03-23 15:25:50Z

2

Alternative using the object Set

new Set(arr).size === 1 // This means all the elements are equal.

let isUniform = (arr) => new Set(arr).size === 1;

console.log(isUniform([4,4,4,4,4]));
console.log(isUniform([4,4,4,4,4,5]));

edited Mar 23, 2019 at 15:25

answered Mar 23, 2019 at 15:20

Ele

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Comments

Nina Scholz · Accepted Answer · 2019-03-23 15:18:39Z

1

Add a return statement with false and end the function. The return value could be used later.

function isUniform(arr) {
    let first = arr[0];
    for (let i = 1; i < arr.length; i++) {
        if (arr[0] !== arr[i]) {
            console.log(false);
            return false;
        }
    }
    console.log(true);
    return true;
}

For using a return value, you need to return true at the end, too.

answered Mar 23, 2019 at 15:18

Nina Scholz

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1 Comment

Ruchi Roy Over a year ago

THANK YOU SO MUCH. Ugh, it's always something stupidly obvious and simple like this.

prasanth · Accepted Answer · 2019-03-23 15:28:02Z

1

Try with Array#every .its Checking all other value is same with first index of array

function isUniform(arr) {
  return arr.every(a=> a === arr[0])
}

console.log(isUniform([2,2,2,2]));
console.log(isUniform([4,4,4,4,4,5]));

answered Mar 23, 2019 at 15:28

prasanth

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Comments

max carin balic · Accepted Answer · 2019-03-23 15:33:42Z

0

The problem is that you need to stop once you've found the first false element:

function isUniform(arr){
    let first = arr[0]; 
    let uniform = true;
    for (let i = 1; i <arr.length; i++){
        if (arr[0] !== arr[i]){
            uniform = false; 
            break;
        }
    } 
    console.log(uniform);
}

edited Mar 23, 2019 at 15:33

answered Mar 23, 2019 at 15:21

max carin balic

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1 Comment

Nina Scholz Over a year ago

break does not prevent to show true. it just exits the loop.

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