I'm trying to flatten nested arrays while preserving the order, e.g. [[1, 2], 3, [4, [[5]]]]
should be converted to [1, 2, 3, 4, 5]
.
I'm trying to use recursion in order to do so, but the code below does not work and I don't understand why. I know there are other methods to do it, but I'd like to know what's wrong with this.
function flatten (arr) {
var newArr = [];
for (var i = 0; i < arr.length; i++) {
if (Array.isArray(arr[i])) {
flatten(arr);
} else {
newArr.push(arr[i]);
}
}
return newArr;
}
flatten([[1, 2], 3, [4, [[5]]]]);
Thanks
The array method accepts an optional parameter depth , which specifies how deep a nested array structure should be flattened (default to 1 ). So to flatten an array of arbitrary depth, just call flat method with Infinity .
To flatten an array means to reduce the dimensionality of an array. In simpler terms, it means reducing a multidimensional array to a specific dimension. let arr = [[1, 2],[3, 4],[5, 6, 7, 8, 9],[10, 11, 12]]; and we need to return a new flat array with all the elements of the nested arrays in their original order.
When calling flatten
recursively, you need to pass arr[i]
to it and then concat the result with newArr. So replace this line:
flatten(arr);
with:
newArr = newArr.concat(flatten(arr[i]));
Here's a common pattern that I regularly use for flattening nested arrays, and which I find a bit more clean due to its functional programming nature:
var flatten = (arrayOfArrays) =>
arrayOfArrays.reduce((flattened, item) =>
flattened.concat(Array.isArray(item) ? flatten(item) : [item]), []);
Or for those who like a shorter, less readable version for code golf or so:
var flatten=a=>a.reduce((f,i)=>f.concat(Array.isArray(i)?flatten(i):[i]),[]);
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