Removing undefined values from Array

Question

In certain situations, it may happen that we have undefined or generally falsy values in Array structures. For instance when reading and filling data f

Answer 1

The solution with Array.filter will actually keep the array unchanged and create a new array without the undesired items. If you want to clean an array without duplicating it, you can use this:

for (var i = data.length-1; i >= 0; i--) {
    if (!data[i]) {
        data.splice(i, 1);
    }
}

Answer 2

in ES6 this can be achieved by simply using using filter with function return the value like this:

const array = [NaN, 0, 15, false, -22, '',undefined, 47, null];
const filteredArr = array.filter(elm => elm);
console.log(filteredArr);

Answer 3

To use Array.prototype.filter here might be obvious. So to remove only undefined values we could call

var data = [42, 21, undefined, 50, 40, undefined, 9];

data = data.filter(function( element ) {
   return element !== undefined;
});

If we want to filter out all the falsy values (such as 0 or null) we can use return !!element; instead.

But we can do it slighty more elegant, by just passing the Boolean constructor function, respectively the Number constructor function to .filter:

data = data.filter( Number );

That would do the job in this instance, to generally remove any falsy value, we would call

data = data.filter( Boolean );

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Since the Boolean() constructor returns true on truthy values and false on any falsy value, this is a very neat option.

Answer 4

You can use lodash compact method, which removes null, undefined and ''

_.compact(data)

Answer 5

Array.prototype.reduce() can be used to delete elements by condition from an array but with additional transformation of the elements if required in one iteration.

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Remove undefined values from array, with sub-arrays support.

function transform(arr) {
    return arr.reduce((memo, item) => {
        if (typeof item !== "undefined") {
            if (Array.isArray(item)) item = transform(item);
            // We can transform item here.
            memo.push(item);
        }
        return memo;
    }, []);
}

let test1 = [1, 2, "b", 0, {}, "", , " ", NaN, 3, undefined, null, 5, false, true, [1, true, 2, , undefined, 3, false, ''], 10];

console.log(transform(test1));

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Try it on jsfiddle.net/bjoy4bcc/

Answer 6

ES6 single line

data.filter(e => e)