Convert a 2D JavaScript array to a 1D array [duplicate]

Question

This question already has answers here:

Merge/flatten an array of arrays (91 answers)

Closed 9 years ago.

I want to convert a 2D JavaScript array to a 1D array, so that each element of the 2D array will be concatenated into a single 1D array.

Here, I'm trying to convert arrToConvert to a 1D array.

var arrToConvert = [[0,0,1],[2,3,3],[4,4,5]];
console.log(get1DArray(arrToConvert)); //print the converted array
function get1DArray(2dArr){
 //concatenate each element of the input into a 1D array, and return the output
 //what would be the best way to implement this function?
}

• Michael Berkowski: Array.join()? developer.mozilla.org/en-US/docs/JavaScript/Reference/…
• Anderson Green: @MichaelBerkowski It looks like Array.join() returns a string instead of an array.
• Michael Berkowski: What is your expected output? Do you mean that you want the 3 sub-arrays flattened into one array? I misunderstood I think.
• Andrew Anderson: Isn't it simple as that arrToConvert.flat()?
• Joel: How would you do this if some elements are arrays and some aren't. For example how would you convert ['a', 'b', 'c', 'd', ['a', 'b', 'c']] to ['a', 'b', 'c', 'd', 'a', 'b', 'c']

Answer 1

Use the ES6 Spread Operator

arr1d = [].concat(...arr2d);

Note that this method is only works if arr2d has less than about 100 000 subarrays. If your array gets larger than that you will get a RangeError: too many function arguments.

For> ~100 000 rows

arr = [];
for (row of table) for (e of row) arr.push(e);

concat() is too slow in this case anyway.

The Underscore.js way

This will recursively flatten arrays of any depth (should also work for large arrays):

arr1d = _.flatten(arr2d);

If you only want to flatten it a single level, pass true as the 2nd argument.

A short < ES6 way

arr1d = [].concat.apply([], arr2d);

• AlThePal78: the underscore way gives me an error when I try to use it on something simple, says that it is undefince
• Blaž Zupančič: @daddycardona underscore.js is an external library. It will be undefined till you import it. underscorejs.org
• Lucas Simões: Just Complementing... ES2019 introduced the .flat() method in Array Prototype. You can pass "depth" paramter in flat() method to specify how deep a nested array structure should be flattened. Defaults to 1.

Answer 2

Try .concat():

var arrToConvert = [[0,0,1],[2,3,3],[4,4,5]];
var newArr = [];
for(var i = 0; i < arrToConvert.length; i++)
{
 newArr = newArr.concat(arrToConvert[i]);
}
console.log(newArr);

Answer 3

Try .reduce()

var test2d = [
 ["foo", "bar"],
 ["baz", "biz"]
];
var merged = test2d.reduce(function(prev, next) {
 return prev.concat(next);
});
console.log(merged)

Source: http://jsperf.com/2-dimensional-array-merge

Answer 4

How about:

var arrToConvert = [[0,0,1],[2,3,3],[4,4,5]];
function get1DArray(arr){
 return arr.join().split(",");
}
console.log(get1DArray(arrToConvert));

http://jsfiddle.net/JRR4J/

• Marty: What happens if the nested elements are objects rather than numbers or strings?
• marteljn: @MartyWallace ["0", "0", "1", "2", "3", "3", "4", "4", "5", "[object Object]"] This is what happens. I see your point my solution will only work with strings and numbers.

Answer 5

var arrToConvert = [[0,0,1],[2,3,3],[4,4,5]];
var modifiedArray = arrToConvert.map(function(array){ 
 return array[0]+array[1]+array[2];
});

Another Example

var passengers = [ 
 ["Thomas", "Meeks"],
 ["Gregg", "Pollack"],
 ["Christine", "Wong"],
 ["Dan", "McGaw"]
];
var modifiedNames = passengers.map(function(convArray){
 return convArray[0]+" "+convArray[1];
});

Answer 6

var arrToConvert = [[0, 0, 1], [2, 3, 3], [4, 4, 5]];
function get1DArray(arr){
 var result = new Array();
 for (var x = 0; x < arr.length; x++){
 for (var y = 0; y < arr[x].length; y++){
 result.push(arr[x][y])
 }
 }
 return result
}
alert (get1DArray(arrToConvert))

http://jsfiddle.net/Saturnix/ReeqQ/