Is there a short way / best practice to concat 3 arrays into 1 array ?
var arr = [],
arr1 = [ 1 , 2 , 3 ],
arr2 = [ 4 , 5 , 6 ],
arr3 = [ 7 , 8 , 9 ];
arr = arr.concat(arr1);
arr = arr.concat(arr2);
arr = arr.concat(arr3);
7 Answers
The shortest (and fastest) solution is arr = arr1.concat(arr2, arr3);
Alternatives:
arr = arr.concat(arr1, arr2, arr3)arr = Array.prototype.concat(arr1, arr2, arr3)arr = [].concat(arr1, arr2, arr3)
2 Comments
TheChrisPratt
One additional alternative
arr = arr1.concat(arr2,arr3)
Radko Dinev
@TheChrisPratt I believe that's what my answer started with.
I would use _.flatten.
var arr = [[1,2,3], [4,5,6], [7,8,9]];
var result = _.flatten(arr) // [1,2,3,4,5,6,7,8,9]
Comments
Spread syntax makes concatenation easy:
arr = [...arr1, ...arr2, ...arr3]
You can even include non-array items inline:
arr = [...arr1, 42, ...arr2, ...arr3]
Comments
There's not much to be done. You can simplify it:
arr = arr.concat(arr1).concat(arr2).concat(arr3)
Or see @Radko Dinev answer for an even simpler (and better) way to do it.
If you have an array of arrays (with a variable number of arrays), you can try:
var m = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
var new_m = [];
new_m.concat.apply(new_m, m);
Comments
_.reduce(arrays, function(result, arr) {
return result.concat(arr)
}, [])
2 Comments
Henrique Barcelos
This solution only woks if OP is using underscore or lodash libraries. Javascript has a native
Array.reduce method for this purpose.
tldr
I end up using lodash for doing map/reduce etc over dictionaries anyway, so I use it for doing these operations over arrays as well. But yeah, you could use Array methods if you don't want to use lodash.
A more flexible way:
var arraysToConcat = [arr1, arr2, arr3];
var arr = Array.prototype.concat.apply([], arraysToConcat);
Comments
If you are here in 2022, there are 3 solutions (with short syntax), a b c are arrays :
let x = [].concat(a, b, c);
let y = [...a, ...b, ...c];
let z = [a, b, c].flat();
Following benchmark :
z is the worst by far.
y is faster with small arrays, but x faster with largest arrays.
With small arrays, it's always fast.
So, we should take the fastest answer with largest arrays : x
arr1+arr2+arr3toconcat