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

It is based on this question: stackoverflow.com/questions/34513679/… — CoderPi
– CoderPi, Commented Dec 29, 2015 at 18:25
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). — Andrue Anderson
– Andrue Anderson, Commented Dec 29, 2015 at 18:27
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
– Joseph Marikle, Commented Dec 29, 2015 at 18:27
@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. — Joseph Marikle
– Joseph Marikle, Commented Dec 29, 2015 at 18:30

Nina Scholz · Accepted Answer · 2015-12-29 20:50:06Z

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>');

edited Dec 29, 2015 at 20:50

answered Dec 29, 2015 at 19:02

Nina Scholz

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Comments

jehna1 · Accepted Answer · 2015-12-29 18:34:36Z

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]);
  }
}

Community · Accepted Answer · 2017-05-23 12:16:06Z

0

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

edited May 23, 2017 at 12:16

CommunityBot

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answered Dec 29, 2015 at 18:32

CoderPi

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3 Comments

Mohamed Taboubi Over a year ago

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 Over a year ago

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 Over a year ago

@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

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