An effective method for transforming a one-dimensional array into a matrix

Question

An effective method for transforming a one-dimensional array into a matrix

My code involves an array that contains subarrays with x-coordinates, y-coordinates, and values representing a matrix:

// [x,y,value]
var arr = [
[1,2,0.01],
[1,3,0.02],
[1,4,0.05],
[1,5,0.03],
[2,3,0.04],
[2,4,0.02],
[2,5,0.01],
[3,4,0.06],
[3,5,0.05],
[4,5,0.07],
]

I also have a 2D array ("matrix") of dimensions x_max X x_max filled with zeroes. I'm attempting to efficiently populate this matrix using the following method:

// assuming 'matrix' is already defined and zero-filled

function constructMatrix(){
    for(var i in arr){
        var y = arr[i][0];
        var x = arr[i][1];
        var val = arr[i][2];
        matrix[y][x] = val;
    }
}

However, my resulting matrix has unique column values but duplicate values across rows. Can you help me identify where my logic might be flawed?

The expected output should resemble the following:

var matrix = [
[0.01,0.02,0.05,0.03],
[0,0.04,0.02,0.01],
[0,0,0.06,0.05],
[0,0,0,0.07],
]

javascript arrays matrix

Answer 1

Answer №1

Here is a way to achieve this:

var arr = [
    [1, 2, 0.01], [1, 3, 0.02], [1, 4, 0.05], [1, 5, 0.03],
    [2, 3, 0.04], [2, 4, 0.02], [2, 5, 0.01], [3, 4, 0.06],
    [3, 5, 0.05], [4, 5, 0.07]
];

// Determine the total number of rows and columns
// Add 1 because (x = 5) == (index 6)    // Indexes start at 0
var rows = arr.reduce((x,y) => Math.max(x, y[0]), 0) + 1;
var columns = arr.reduce((x,y) => Math.max(x, y[1]), 0) + 1;

// Create an empty matrix 
var matrix = [...Array(rows)].map(() => Array(columns).fill(0));

// Iterate over the points
arr.forEach(function(point) {
    var x = point[0];
    var y = point[1];
    var val = point[2];
    matrix[x][y] = val;
});

// Display the result
console.log(  JSON.stringify(matrix, 0, 2)  );

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

Answer 2

Here is a way to achieve this:

var arr = [
    [1, 2, 0.01], [1, 3, 0.02], [1, 4, 0.05], [1, 5, 0.03],
    [2, 3, 0.04], [2, 4, 0.02], [2, 5, 0.01], [3, 4, 0.06],
    [3, 5, 0.05], [4, 5, 0.07]
];

// Determine the total number of rows and columns
// Add 1 because (x = 5) == (index 6)    // Indexes start at 0
var rows = arr.reduce((x,y) => Math.max(x, y[0]), 0) + 1;
var columns = arr.reduce((x,y) => Math.max(x, y[1]), 0) + 1;

// Create an empty matrix 
var matrix = [...Array(rows)].map(() => Array(columns).fill(0));

// Iterate over the points
arr.forEach(function(point) {
    var x = point[0];
    var y = point[1];
    var val = point[2];
    matrix[x][y] = val;
});

// Display the result
console.log(  JSON.stringify(matrix, 0, 2)  );

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

Answer 3

Answer №2

If you are referring to the point (1,2) as the first column and second row in a grid, then the correct assignment would be:

matrix[y - 1][x - 1] = val

This adjustment accounts for the fact that coordinates begin at 0,0 and go up to 4,4 on a 5x5 matrix.

Answer 4

If you are referring to the point (1,2) as the first column and second row in a grid, then the correct assignment would be:

matrix[y - 1][x - 1] = val

This adjustment accounts for the fact that coordinates begin at 0,0 and go up to 4,4 on a 5x5 matrix.

An effective method for transforming a one-dimensional array into a matrix

Answer №1

Answer №2

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