CODEWITHSUNDEEP
javascriptloops
Stephan - the curious
Stephan - the curious

Reputation: 423

I wonder if I can compare two array items without an if-statement

given that I want to compare two equally long arrays, if they have the same value at the same position, can I do this with a loop but with NO IF STATEMENT?

This code works

function twoArrays(arr, arr2) {
    var count = 0;
    arr.forEach (function(item, index){
        if(arr[item, index]===arr2[item, index]) {
            count++
        }
    })
    return count
}

twoArrays([2,3,4,6],[2,1,4,5])
// return 2

But how about something without an if statement?

EDIT: every time there is a match the counter goes up one. Bonus: can I use other loops? (Which)?

Upvotes: 1

Views: 48

Answers (1)

T.J. Crowder
T.J. Crowder

Reputation: 1074465

There are a couple of ways to avoid an if statement, though it's not clear why you want to.

The first is to use filter:

var count = arr1.filter(function(item, index) { return item === arr2[index]; }).length;

...but it creates an unnecessary array (temporarily).

Live Example:

function twoArrays(arr1, arr2) {
    return arr1.filter(function(item, index) { return item === arr2[index]; }).length;
}
console.log(twoArrays([2,3,4,6],[2,1,4,5]));

The second is to use &&:

var count = 0;
arr1.forEach(function(item, index) { item === arr2[index] && ++count; });

...but it's really just an if in disguise. && evaluates its left-hand operand and, if that operand is falsy, takes that falsy value as its result (which is then thrown away in the above); if the value of the left-hand operand is truthy, && evaluates its right-hand operand and takes that as its result. That means side effects in the right-hand operand only happen if the left-hand operand's value is truthy, which is why ++count works.

Live Example:

function twoArrays(arr1, arr2) {
    var count = 0;
    arr1.forEach(function(item, index) { item === arr2[index] && ++count; });
    return count;
}
console.log(twoArrays([2,3,4,6],[2,1,4,5]));

Similarly, you could use the conditional operator, either with forEach:

var count = 0;
arr1.forEach(function(item, index) { count += item === arr2[index] ? 1 : 0; });

...or with reduce:

var count = arr1.reduce(function(acc, item, index) { return acc + (item === arr2[index] ? 1 : 0); }, 0);

Live Example:

function twoArraysA(arr1, arr2) {
    var count = 0;
    arr1.forEach(function(item, index) { count += item === arr2[index] ? 1 : 0; });
    return count;
}
console.log(twoArraysA([2,3,4,6],[2,1,4,5]));

function twoArraysB(arr1, arr2) {
    return arr1.reduce(function(acc, item, index) { return acc + (item === arr2[index] ? 1 : 0); }, 0);
}
console.log(twoArraysB([2,3,4,6],[2,1,4,5]));

...but again, there's still conditional logic in there.

I don't recommend any of them. Just use the if. :-)

Upvotes: 2

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