I'm trying to write a function isUniform()

Question

The function should take an array, and compare the first item in an array with others. Eventually, it should print on console "True" if all the items an an array the same, and "False" otherwise. My function does the following:

function isUniform(list) {
    var firstItem = list[0];
    for (var i = 0; i <=list.length; i++){
        i++
        if(firstItem === list[i]){
            console.log("True");
        }else {
            console.log("False");
        };
    };
}


input:
isUniform(['a','a','a'])
**********************
output:
VM512:6 True
VM512:8 False

Could you please give me some insight on what I should change?

score 1 · Answer 1 · answered Mar 11 '20 at 13:09

1

The correct algorithm for what you try to achieve is:

function isUniform (list) {
    var firstItem = list[0];
    for (var i = 0; i < list.length; i++){
        if (firstItem === list[i]) {
            console.log("True");
        } else {
            console.log("False");
        };
    };
}

isUniform(['a','a','a'])

You don't need to increment your i in your for loop, the loop already does that. And you need to iterate until i < list.length, not i <= list.length, that is why you got a false log at the end, you are out of your array. So the condition is firstItem === undefined.

https://jsfiddle.net/9L20engu/

answered Mar 11 '20 at 13:09

Zooly

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Thanks, but your algorithm doesn't work with a wrong input, try it with isUniform([1,2,3,5]). It behaves the same way... – Mukhammad Sobirov Mar 11 '20 at 13:18
`isUniform([1,2,3,5])` prints True, False, False, False. Because first item equals 1, and not the followings. Algorithm works. – Zooly Mar 11 '20 at 13:24
i gotta figure out the way to print just one "True" or "False" for the entire function. – Mukhammad Sobirov Mar 11 '20 at 13:37
got it! I wasn't supposed to console.log("True")... should have used return true – Mukhammad Sobirov Mar 11 '20 at 13:45

Keith · Accepted Answer · 2020-03-11T13:28:44.780

You could use Array.every https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/every, to make sure every item is the same as the first..

But a more optimal version would be Array.some, https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some This is because it can then early terminate the loop. The logic is slightly reversed, with having to do a double inequality check.

I've also included using a for loop, more akin to OP's knowledge.

eg.

//use every, this is saying make sure every item is the same as first
//but does mean every item needs traversing
function isUniform(list) {
  const firstItem = list[0];;
  return list.every(i => i === firstItem);
}

//using some we could early terminate the loop by stopping at the first
//item that is not equal,.  and then NOT the result.
function isUniform2(list) {
  const firstItem = list[0];;
  return !list.some(i => i !== firstItem);
}

//using a good old for loop
//this is basically working like the Array.some, basically compare each item
//to the first, once we get a difference return false, if we make it all the
//way through the array, it must mean there all equal.
function isUniform3(list) {
  var firstItem = list[0];
  for (var i = 0; i < list.length; i++){
    if (firstItem !== list[i]) return false;
  }
  return true;
}



console.log('using every');
console.log(isUniform(['a','a','a']));
console.log(isUniform(['a','b','a']));
console.log('using some');
console.log(isUniform2(['a','a','a']));
console.log(isUniform2(['a','b','a']));
console.log('for loop');
console.log(isUniform3(['a','a','a']));
console.log(isUniform3(['a','b','a']));

Would `some` be more efficient? Returns false if array empty, stop at first non-condition check — Zooly, Mar 11 '20 at 13:12
Great solution, but I didn't cover these methods yet. Wanted to solve the task with the knowledge that I currently have. Thanks for your solution! — Mukhammad Sobirov, Mar 11 '20 at 13:22
@MukhammadSobirov NO problem, I'll do a update that works using for loop. Give us a tick. — Keith, Mar 11 '20 at 13:24
@MukhammadSobirov Ok, updated with for loop, so it's very similar to your version. — Keith, Mar 11 '20 at 13:27

I'm trying to write a function isUniform()

2 Answers2