Transposing variable size array in javascript?

Question

I am trying to get my 2D array to export as a .csv file. My array is in the form: [[1,2],[],[3],[4,5,6]]. I would like the spreadsheet to be formatted as

    h1 h2 h3 h4
    1     3  4
    2        5
             6

I cannot change the format I receive the data in. I've looked into ways to transpose the array but the solutions I've seen don't work with variable size arrays like mine. So far my only idea (in psuedoish code) is:

    for (i < length of longest column; i++) {
         var arr = [];
         if (i > col1.length) arr.push("");
         else arr.push(col1[i]);
         //so on for rest of cols
         csvFile += arr;
    }

Is there a better way to do it?

Nina Scholz · Accepted Answer · 2018-06-13 19:14:24Z

1

You could transpose the array by using arrays with the length of the outer array as length for every line.

var array = [[1, 2], [], [3], [4, 5, 6], [,,7]],
    result = array.reduce((r, a, i, { length }) => {
        a.forEach((v, j) => {
            r[j] = r[j] || new Array(length).fill('');
            r[j][i] = v;
        });
        return r;
    }, []);
    
console.log(result);

edited Jun 13, 2018 at 19:14

answered Jun 13, 2018 at 18:33

Nina Scholz

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Washington Guedes · Accepted Answer · 2018-06-13 19:04:01Z

1

You are almost there, just missing the inner loop (because a CSV table has rows X columns):

var input = [[1,2],[],[3],[4,5,6]];

var lengthOfLongestColumn = Math.max(...input.map(a => a.length));
var csvFile = [['h1','h2','h3','h4']];

for (var i = 0; i < lengthOfLongestColumn; i++) {
    var row = [];
    
    for (var j = 0; j < input.length; j++) {
        var col = input[j];
        
        if (i >= col.length) {
            row.push('');
        }
        else {
            row.push(col[i]);
        }
    }
    csvFile.push(row);
}

console.log(csvFile)

answered Jun 13, 2018 at 19:04

Washington Guedes

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