Build arrays using an array (javascript)

Question

How may I build a function in javascript that do the following :

Input :

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

output:

dataset = [ 
[null, 1, 2, 3, null, null, null, null, null],
[null, null, null, null, null, null, 2, null, null],
[null, null, null, null, null, null, null, null, 4], 
]

in fact in this example, my input have 3 set of no null values : these sets are : [1, 2, 3], [2] and [4]

from these sets I want builds arrays that have these values (of not null sets) and that conserve the same index as the input array

---

Thank you

• Lee Taylor: Can you explain how the input becomes the output?
• CoderPi: It is based on this question: stackoverflow.com/questions/34513679/…
• Andrue Anderson: How would you know, @CodeiSir? I believe it would be frowned upon to have multiple accounts as one could be tempted to up-vote one's own question(s).
• Joseph Marikle: the input to output doesn't make any sense. Why does the first one arbitrarily retain three non-null values when the other two arrays only retain one each?
• Joseph Marikle: @PraveenKumar I assumed the same, but it doesn't make sense where the array splits off to a new row. I could understand one non-null value per row, or even splitting it into thirds, but neither of those work.

Answer 1

Just a proposal with Array.prototype.reduce()

var data = [null, 1, 2, 3, null, null, 2, null, 4],
 result = [];
data.reduce(function (r, a, i) {
 if (a !== null) {
 if (r === null) {
 result.push(Array.apply(null, { length: data.length }).map(function () { return null; }));
 }
 result[result.length - 1][i] = a;
 }
 return a;
}, null);
document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

Answer 2

Here's my result:

var data = [null, 1, 2, 3, null, null, 2, null, 4];
var dataset = [[]];
for(var i = 0; i < data.length; i++) {
 if(!data[i]) {
 if(!data[i-1]) {
 dataset[dataset.length-1].push(data[i]);
 } else {
 for(var fillRight = i; fillRight < data.length; fillRight++) {
 dataset[dataset.length-1].push(null);
 }
 dataset.push([null]);
 for(var fillLeft = 0; fillLeft < i; fillLeft++) {
 dataset[dataset.length-1].push(null);
 }
 }
 } else {
 dataset[dataset.length-1].push(data[i]);
 }
}

Answer 3

Here you are..

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

based on this answer: https://stackoverflow.com/a/34513955/4339170

I only added the lines:

 if(b.length) b[b.length-1] = b[b.length-1].concat(Array(a.length-i).map(function(){return null}))
 b.push(arr = Array.apply(null, Array(i)).map(function() {return null}));

where the first fills up the end with nulls when a section is done, and the second fills up the front of a new section with nulls

• Mohamed Taboubi: Hi CodeiSir, Good thank you, however it does not do the all the job : The result I got is this : [null, 1, 2, 3, undefined × 5] [null, null, null, null, null, 2, undefined × 2] [null, null, null, null, null, null, null, null, 4] I guess the result table should be filled by null before enter the loop ?
• CoderPi: Well you could also fill up an array with nulls first and then just place the new items at the correct position. Would be more performant, by I don't have the time right now
• CoderPi: @taboubim it gives me [[null,1,2,3,null,null,null,null,null],[null,null,null,null,null,2,null,null],[null,null,null,null,null,null,null,null,4]] as you can see in the output