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up vote 7 down vote favorite

Imagine I have an array

A = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)

And I want it to convert into 2-dimensional array (matrix of N x M), for instance like this:

A = Array(Array(1, 2, 3), Array(4, 5, 6), Array(7, 8, 9))

Note, that rows and columns of the matrix is changeable.

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4 Answers 4

up vote 11 down vote accepted

Something like this?

function listToMatrix(list, elementsPerSubArray) {
    var matrix = [], i, k;

    for (i = 0, k = -1; i < list.length; i++) {
        if (i % elementsPerSubArray === 0) {
            k++;
            matrix[k] = [];
        }

        matrix[k].push(list[i]);
    }

    return matrix;
}

Usage:

var matrix = listToMatrix([1, 2, 3, 4, 4, 5, 6, 7, 8, 9], 3);
// result: [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
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1  
Exactly what I needed. Thanx man. –  Bakhtiyor Dec 20 '10 at 18:05
1  
@Bakhtiyor: Glad if it helped ;) –  elusive Dec 20 '10 at 18:09
up vote 1 down vote

Simply use two for loops:

var rowNum = 3;
var colNum = 3;
var k = 0;
var dest = new Array(rowNum);

for (i=0; i<rowNum; ++i) {
  var tmp = new Array(colNum);
  for (j=0; j<colNum; ++j) {
    tmp[j] = src[k];
    k++;
  }
  dest[i] = tmp;
}
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Could you re-write it in C# please? –  Clark Kent Oct 12 '11 at 22:03
up vote 2 down vote 
function matrixify( source, count )
{
    var matrixified = [];
    var tmp;
    // iterate through the source array
    for( var i = 0; i < source.length; i++ )
    {
        // use modulous to make sure you have the correct length.
        if( i % count == 0 )
        {
            // if tmp exists, push it to the return array
            if( tmp && tmp.length ) matrixified.push(tmp);
            // reset the temporary array
            tmp = [];
        }
        // add the current source value to the temp array.
        tmp.push(source[i])
    }
    // return the result
    return matrixified;
}

If you want to actually replace an array's internal values, I believe you can call the following:

source.splice(0, source.length, matrixify(source,3));
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up vote 2 down vote

How about something like:

var matrixify = function(arr, rows, cols) {
    var matrix = [];
    if (rows * cols === arr.length) {
        for(var i = 0; i < arr.length; i+= cols) {
            matrix.push(arr.slice(i, cols + i));
        }
    }

    return matrix;
};

var a = [0, 1, 2, 3, 4, 5, 6, 7];
matrixify(a, 2, 4);

http://jsfiddle.net/andrewwhitaker/ERAUs/

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