Convert 1D array index to 2D array index

Question

I have 2 arrays. I want to convert the index of the first array to the second. Is there a better way to do it than what I have below?

Array array1[9];
Array array2[3][3];

// Index is the index of the 1D array
public Point convert1Dto2D(int index)
{
        Point p = new Point();

        switch (index) {
            case 0:
                p.x = 0;
                p.y = 0;
                break;
            case 1:
                p.x = 0;
                p.y = 1;
                break;
            case 2:
                p.x = 0;
                p.y = 2;
                break;
            case 3:
                p.x = 1;
                p.y = 0;
                break;
            case 4:
                p.x = 1;
                p.y = 1;
                break;
            case 5:
                p.x = 1;
                p.y = 2;
                break;
            case 6:
                p.x = 2;
                p.y = 0;
                break;
            case 7:
                p.x = 2;
                p.y = 1;
                break;
            case 8:
                p.x = 2;
                p.y = 2;
                break;
        }

return p;
}

Sapph · Accepted Answer · 2011-03-31 03:18:56Z

54

p.x = index / 3;
p.y = index % 3;

answered Mar 31, 2011 at 3:18

Sapph

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4 Comments

vexe Over a year ago

@PeterOlson Why does it matter?

Peter Olson Over a year ago

@vexe It's been 3 years since I made that comment, so I don't remember exactly what I had in mind. I imagine it had more to do with being conventional than being correct.

X3R0 Over a year ago

x, y, then z. its always has been and always will be

Justiniscoding Over a year ago

If you're using this solution in a different programming language, make sure to round the x index down to the nearest whole number. You don't have to in C# because it excludes decimals from the result of the division of two integers, while languages like javascript do not.

Chris Taylor · Accepted Answer · 2011-03-31 03:18:51Z

11

You can do this mathematically using modulus and integer division, given your second array is a 3x3 array the following will do.

p.y = index % 3;
p.x = index / 3;

answered Mar 31, 2011 at 3:18

Chris Taylor

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Comments

Razor · Accepted Answer · 2011-03-31 03:33:03Z

2

I assume your running that code in a loop? If so

IEnumerable<Point> DoStuff(int length, int step) {
    for (int i = 0; i < length; i++)
        yield return new Point(i/step, i%step);
}

Call it

foreach (var element in DoStuff(9, 3))
    {
        Console.WriteLine(element.X);
        Console.WriteLine(element.Y);
    }

answered Mar 31, 2011 at 3:33

Razor

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Comments

Ska · Accepted Answer · 2019-02-07 10:11:47Z

2

Just in case someone wonders for Javascript.

var columnCount = 3
for(var i=0; i < 10; i++){
  var row = Math.floor(i/ columnCount )
  var col = i % columnCount 
  console.log(i, row, col)
}

edited Feb 7, 2019 at 10:11

answered Feb 7, 2019 at 9:07

Ska

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