Merge and sort an array of numbers in numerical order - javascript

Question

I am trying to merge and sort 2 arrays in numerical order.

function merge_arrays(a, b) {
    console.log( (a.concat(b)).sort().join(" ") );
}

This works fine with single digits in an array, but it doesn't sort numbers with double digits properly.

eg:

a: [2, 3, 7, 8, 8,]

b: [7, 8, 13]

will output as: 13 2 3 7 7 8 8 8

Am I missing something?

Answer 1

Quoting from MDN :

The default sort order is lexicographic (not numeric).

Try this instead:

function merge_arrays(a, b) {
    console.log( (a.concat(b)).sort(function(a, b) { return a - b; }).join(" ") );
}

Answer 2

http://www.w3schools.com/jsref/jsref_sort.asp

See that section Note: When numbers are sorted alphabetically, "40" comes before "5".

To perform a numeric sort, you must pass a function as an argument when calling the sort method.

The function specifies whether the numbers should be sorted ascending or descending.

Meaning This

function numOrdA(a, b){ return (a-b); }

and your code :

a.concat(b)).sort(numOrdA).join(" ")

Answer 3

Try this:

c = a.concat(b)
c == [2,3,7,8,8,7,8,13]
c.sort() == [13,2,3,7,7,8,8,8]

This is because, when not provided with a comparison function, sort automatically converts the elements of the list it is sorting to strings. In string land "13" < "2".

Check out the sort documentation .

So what you probably want is something like this:

function compare_number(a,b) {
    return a - b;
}

a.concat(b).sort(compare_number);

And to fully answer your question:

a.concat(b).sort(compare_int).join(" ");