How to remove empty columns in 2D Array in Javascript efficiently

Question

I have following array of arrays (2D Array)

Input    csvData = [["", "2", "",  ""], ["", "3", "", ""], ["", "", "4", ""]]

How to remove empty columns from above array.

   Output   csvData = [[ "2", ""], ["3", ""], ["","4"]]

I am trying but not able to complete.

  removeEmptyColumns(csvData) {
    for (let i = 0; i < csvData.length; i++) {
      let col = csvData.map(function (value, index) { return value[i]; });
      for (let j = 0; j < col.length; j++) {
        if (col[j])
          break;
      }

    }

  }

I would consider the slice method (w3schools.com/jsref/jsref_slice_array.asp) for efficiency and maintainability. — Sam
– Sam, Commented Mar 9, 2019 at 22:55
I don't understand, shouldn't the output be: csvData = [[ "2", ""], ["3", ""], ["", "4"]]? — ibrahim mahrir
– ibrahim mahrir, Commented Mar 9, 2019 at 23:02

Nina Scholz · Accepted Answer · 2019-03-10 08:52:55Z

5

You could get first the filled column and then filter the arrays.

var csvData = [["", "2", "",  ""], ["", "3", "", ""], ["", "", "4", ""]],
    columns = csvData.reduce(
        (r, a) => (a.forEach((v, i) => r[i] = r[i] || v), r),
        []
    );

csvData = csvData.map(a => a.filter((_, i) => columns[i]));

console.log(csvData);

.as-console-wrapper { max-height: 100% !important; top: 0; }

For deleting only the last empty columns, you could get the max value of the filled columns and delete the rest.

var csvData = [["", "2", "",  ""], ["", "3", "", ""], ["", "", "4", ""]],
    max = csvData.reduce(
        (r, a) => (a.forEach((v, i) => v && (r = Math.max(r, i))), r),
        0
    );

csvData = csvData.map(a => a.slice(0, max + 1));

console.log(csvData);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Mar 10, 2019 at 8:52

answered Mar 9, 2019 at 22:59

Nina Scholz

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3 Comments

Sreekanth Reddy Over a year ago

What is the time complexity for the above answer? Is there any edge cases it can fail?

Nina Scholz Over a year ago

at least O(2n).

Sreekanth Reddy Over a year ago

could you please solve my another complex problem. stackoverflow.com/questions/55083788/…

Ori Drori · Accepted Answer · 2019-03-09 23:12:51Z

2

Use Array.reduce() with Array.some() to identify empty columns.

Then use Array.map() to iterate the array, and Array.filter() to remove the items at the empty columns.

const removeEmptyColumns = arr => {
  // detect empty columns
  const emptyColumns = (arr[0] || []).map((c, i) => arr.some(a => a[i]))
  
  // filter empty columns
  return arr.map(a => a.filter((_, i) => emptyColumns[i]))
}

pp(removeEmptyColumns([["", "2", "",  ""], ["", "3", "", ""], ["", "", "4", ""]]))

pp(removeEmptyColumns( [["1", "2", "", "4"], ["", "3", "", ""], ["", "", "", "2"]]
))

function pp(d) {
  console.log(JSON.stringify(d))
}

edited Mar 9, 2019 at 23:12

answered Mar 9, 2019 at 22:52

Ori Drori

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1 Comment

Sreekanth Reddy Over a year ago

Droi, Could you please try to solve my another complex problem stackoverflow.com/questions/55083788/…

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