How do I concatenate arrays based on their size in JavaScript?

Question

I have four arrays A,B.C, and D. For example:

length of A is 1 
length of b is 4 
length of C is 1
length of D is 2.

var a = [1];
var b = [2,3,4,5];
var c = [6];
var d = [7,8];

I want to concat those four arrays based on the larger length of the arrays, so the arrays will be in order: b,d,a,c:

Expected result:

[2,3,4,5,7,8,1,6]
[2,3,4,5,1,6,7,8] //also valid, a and c are same length, so can be sorted this way too.

How can I find the larger to lower arrays and concat them from larger to smaller in JavaScript?

Answer 1

Mine's more verbose but still seems to work; the idea in all first 3 answers is to put the arrays into an additional array, then do a custom sort of the arrays based on their length. A good if somewhat dated reference is at: http://www.javascriptkit.com/javatutors/arraysort.shtml

var arrays = [a, b, c, d];
var concatentation = [];

arrays.sort(function(x, y) {
    return y.length - x.length;    
});

for (var i=0, n=arrays.length; i<n; i++) {
    concatentation = concatentation.concat(arrays[i]);
}

console.log(concatentation); //[2, 3, 4, 5, 7, 8, 1, 6]

Answer 2

It's simple enough using sort and concat:

Array.prototype.concat.apply([], [a, b, c, d].sort(function (a, b) {
  return b.length - a.length;
}));

Array.prototype.concat.apply is used to join the child arrays together.

Answer 3

You could do this quite neatly with underscore:

_.sortBy([a,b,c,d], function(num) { 
    return num.length; 
}).reverse().join(',').split(',');