Split Array using Null separator

Question

Is there a method to split an array into arrays that dont contain null values using javascript (without developing a function)...

Here is an example of what I want have :

input :

var a = [1, 2, 3, null, 2, null,null, 4]

output :

[[1, 2, 3], [2], [4]]

Thank you

• Tushar: Have you tried to loop over array and create sub arrays?
• Mohamed Taboubi: I know I can, but I'm asking if there is a ready method for use ... without developing a function
• Denys Séguret: Looping is done in about 3 lines and there's no reason there would be a generic solution to this very specific problem.
• Mohamed Taboubi: Ok, that's fine so ... (the split function for strings is awesome -- I hoped there is one for arrays) ... Thank you
• CoderPi: A loop is the best you can do

Answer 1

To the question

"Is there a ready to use function to build my array",

the answer is

"No, because your need is too specific".

But it's not so hard to do it yourself. Here's a solution (I took a less trivial input with null at ends and consecutive null to be more demonstrative):

var a = [null, 1, 2, 3, null, 2, null, null, 4, null];
var b = []; // result
for (var arr, i=0; i<a.length; i++) {
 if (a[i]===null) {
 arr=null;
 } else {
 if (!arr) b.push(arr=[]);
 arr.push(a[i]);
 }
}
document.body.textContent = JSON.stringify(b); // just print the result
 

As you can see, there's nothing pretty or magical, just a tedious iteration.

• Mohamed Taboubi: Yes, Thanks Denys, this works .. but my question is about if there is a method ready for use or not ... However I know that we can develop a function :) ... thank you for your help
• Mohamed Taboubi: Thank you Denys .. I took your answer as the accepted one :)
• CoderPi: using slice would be faster I think
• Denys Séguret: @CodeiSir depending on the input, it would probably be faster, yes, but push is already fast (especially on homogeneous arrays) so I doubt it really matters (but I agree it could be faster).

Answer 2

You can use reduce:

[1, 2, 3, null, 2, null, 4].reduce(function(arr, val) {
 if(val === null) arr.push([]);
 else arr[arr.length-1].push(val);
 return arr;
}, [[]]);

• Denys Séguret: that's the general idea but this doesn't handle painful cases like a null at the begining or two consecutive null.
• Oriol: @DenysSéguret "_".split("_") is ["",""]. Similarly, my code returns [ [],[] ] for [null].
• Mohamed Taboubi: Also, this function is not good, for example if I have in input : [1, 2, 3, null, 2, null,null,null, 4]
• James Thorpe: @taboubim If that's the case, you need to make your question clearer about possible inputs and expected outputs, though if you do, you may invalidate this answer. A better approach may be to take this as an answer to the question asked, and see if you can tweak it to suit your actual needs.
• Oriol: @DenysSéguret "123_2___4".split("_") is ["123","2","","","4"]. Similarly, my code returns [[1,2,3],[2],[],[],[4]] for [1,2,3,null,2,null,null,null,4].

Answer 3

There is no function in the library which does what you expect. But if you approach it simply, you can use the next approach

var a = [1, 2, 3, null, 2, null, 4]
var result = [], temp = [];
for(var i = 0; i < a.length; i++) {
 if (a[i] === null) {
 if (temp.length == 0) continue;
 result.push(temp);
 temp = [];
 }
 else {
 temp.push(a[i]);
 }
}
if (temp.length != 0) result.push(temp);
// use your result, it gives [[1, 2, 3], [2], [4]]

i have added some functionalities to prevent problems with double null, starting null and ending null. The next step is just wrapping the above snippet in a function, using a as argument and result as return value. This even handles a = [] without problems too.

Answer 4

I needed this function, and using .push() isn't going to be fast enough. Here's one using .slice(), as coderPi pointed out.

function split(arr, separator = null) {
 const chunks = [];
 let i = 0, j = 0;
 while (j++ < arr.length) {
 let nextIndex = arr.indexOf(separator, i);
 if (nextIndex === -1) {
 chunks.push(arr.slice(i, arr.length));
 return chunks;
 } else if (nextIndex !== i) {
 chunks.push(arr.slice(i, nextIndex));
 }
 i = nextIndex + 1;
 }
 return chunks;
}
// example:
const myChucks = split([1, 2, 3, null, 2, null, null, 4]);
// returns: [[1,2,3],[2],[4]]
document.write(JSON.stringify(myChucks))