JavaScript Code to Calculate Match Percentage in an Array

Array.prototype.some()

The some() method tests whether at least one element in the array passes the test implemented by the provided function. But it does not provide us any information on how many items match or all of them match. In fact, as soon as the first item is matched, it returns true (condition is not evaluated for all the array elements).

But what if we have a scenario where want to identify if

• all of them matched, or
• at least half of them matched, or
• percentage of matching elements.

Curious to know how can we do it?

Here is a simple match function that we can use with reduce to find out the exact matching percentage.

function match(fx) {
    return function(pv, current, index, array) {
    const fc = fx(current) ? 1 : 0;
    if(index === 1) {
        const fp = fx(pv) ? 1 : 0;
        return fp + fc;
    }
    if(index === array.length - 1) {
        return (pv + fc)/array.length;
    }
    return pv + fc;
  }
}

Output:

// how many items are greater than zero, 

console.log(
  [1].reduce(match(x => x > 0)) 
);  //1 i.e. 100%                                                                               
console.log(
  [0, 1].reduce(match(x => x > 0))
);  //1 i.e. 100%
console.log(
  [2, 4, 6].reduce(match(x => x % 2 === 0))
); //1 i.e. 100%
console.log(
  [2, 4, 6, 3].reduce(match(x => x % 2 === 0))
); //0.75 i.e. 75%
console.log(
  [2, 4, 6, 3, 5].reduce(match(x => x % 2 === 0))
); //0.6 i.e. 60%

Wondering what would be the practical use of this? Machine learning algorithms often depend upon match percentage of different criteria, where such code implementation can be handy.

Hope this helps!