What is the reason behind the one-way functionality of underscore's difference method?

Question

What is the reason behind the one-way functionality of underscore's difference method?

If I asked you, "What separates these two arrays: ['a'] and ['a', 'b']?" your answer would be 'b', correct?

I'm curious why underscore doesn't automatically provide bidirectional diff functionality. How can we use other methods to achieve this result?

var x = ['js-email'],
    y = ['js-email', 'form-group'],
    z = _.difference(x, y), // outcome: []
    w = _.difference(y, x); // outcome: ["form-group"]

Check out this example on JSFiddle.

To clarify, I want the difference between the arrays to always be ['form-group'], regardless of their order.

javascript arrays underscore.js difference

Answer 1

Answer №1

To find the unique elements between two sets, you can simply combine the differences in both directions.

function getUniqueElements(firstSet, secondSet) {
    return _.union(_.difference(firstSet, secondSet), _.difference(secondSet, firstSet));
}

console.assert(getUniqueElements(["a", "b"], ["a", "c"]).toString() == "b,c");
var setA = ["js-email"], setB = ["js-email", "form-group"];
console.assert(getUniqueElements(setA, setB).toString() == "form-group");

If you wish to incorporate this function into the _ library itself for easy access throughout your project, you can use the _.mixin method like this:

_.mixin({
    getUniqueElements: function(firstSet, secondSet) {
        return _.union(_.difference(firstSet, secondSet), _.difference(secondSet, firstSet));
    }
});

Then you can call the function like this:

console.assert(_.getUniqueElements(["a", "b"], ["a", "c"]).toString() == "b,c");
var setA = ["js-email"],
    setB = ["js-email", "form-group"];
console.assert(_.getUniqueElements(setA, setB).toString() == "form-group");

Answer 2

To find the unique elements between two sets, you can simply combine the differences in both directions.

function getUniqueElements(firstSet, secondSet) {
    return _.union(_.difference(firstSet, secondSet), _.difference(secondSet, firstSet));
}

console.assert(getUniqueElements(["a", "b"], ["a", "c"]).toString() == "b,c");
var setA = ["js-email"], setB = ["js-email", "form-group"];
console.assert(getUniqueElements(setA, setB).toString() == "form-group");

If you wish to incorporate this function into the _ library itself for easy access throughout your project, you can use the _.mixin method like this:

_.mixin({
    getUniqueElements: function(firstSet, secondSet) {
        return _.union(_.difference(firstSet, secondSet), _.difference(secondSet, firstSet));
    }
});

Then you can call the function like this:

console.assert(_.getUniqueElements(["a", "b"], ["a", "c"]).toString() == "b,c");
var setA = ["js-email"],
    setB = ["js-email", "form-group"];
console.assert(_.getUniqueElements(setA, setB).toString() == "form-group");

Answer 3

Answer №2

.difference works similarly to PHP's array_diff and similar functions by returning items that exist in the first array but not in any of the other arrays passed to it.

It's important to note that "the things in a that aren't in b" is not the same as "the things in b that aren't in a", which is why this behavior is intentional.

To achieve a bidirectional difference, you will need to run the function in both directions and then remove duplicates from the final result.

Answer 4

.difference works similarly to PHP's array_diff and similar functions by returning items that exist in the first array but not in any of the other arrays passed to it.

It's important to note that "the things in a that aren't in b" is not the same as "the things in b that aren't in a", which is why this behavior is intentional.

To achieve a bidirectional difference, you will need to run the function in both directions and then remove duplicates from the final result.

Answer 5

Answer №3

_.differencecan take in multiple arrays as input:

It works like excluding elements present in other arrays and only keeping unique values from the original array

This function is intended for one-way operations.

Answer 6

_.differencecan take in multiple arrays as input:

It works like excluding elements present in other arrays and only keeping unique values from the original array

This function is intended for one-way operations.

What is the reason behind the one-way functionality of underscore's difference method?

Answer №1

Answer №2

Answer №3

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