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spudw2k

Map Index to 2D Array

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spudw2k

I was reading a recent post about converting a 2D array into a 1D array.  The OP, from my understanding, more-or-less wanted to extract a single column of data and format it in a 1D array.  The solutions were proper and efficient compared to what I wanted to share, but I figured I'd share as it's a good lesson and a neat, purely mathematical approach to mapping an index to a 2D array.  As-is, this only works for 2D arrays.  

By knowing how big a 2D array is, an index can be calculated for each indices/subscript.  The functions below define a random sized 2D array, and calculate an index that matches the indices on the 2D array.

#include "Array.au3"
$iRow = Random(2,10,1)
$iCol = Random(2,10,1)
$iRandomIndex = Random(0,($iRow*$iCol)-1,1)

$sIndicies = _IndexTo2DIndicies($iRandomIndex, $iRow, $iCol)
_2DArrayTo1DIndexes($iRow, $iCol, $iRandomIndex & " = $aArr" & $sIndicies)


Func _2DArrayTo1DIndexes($iRow = 1, $iCol = 1, $sMsg = Default)
    $iRow = Int($iRow)
    $iCOl = Int($iCol)
    Local $aData[$iRow][$iCol]

    For $iY = 0 to $iRow - 1
        For $iX = 0 to $iCol - 1
            Local $iIndex
            ;Index = ($iColMax * $iY) + $iX
            $aData[$iY][$iX] = ($iCol * $iY) + $iX
        Next
    Next

    If $sMsg = Default Then $sMsg = "1D Indexes of 2D Array Indicies"
    _ArrayDisplay($aData,$sMsg)
EndFunc

Func _IndexTo2DIndicies($iIndex = 0, $iRow = 0, $iCol = 0)
    $iIndex = Int($iIndex)
    $iRow = Int($iRow)
    $iCol = Int($iCol)

    If $iIndex = 0 Then Return "[0][0]"
    If $iIndex >= $iRow * $iCol Then Return SetError(1,0,0)

    Local $iX = Mod($iIndex, $iCol)
    ;Local $iY = ($iIndex-$iX) / $iCol
    Local $iY = Int($iIndex / $iCol)    ;Thanks Chimp

    Return "[" & $iY & "][" & $iX & "]"
EndFunc

I used this type of approach before with a pixel array.  I had a 1D array for storing individual pixel information, then mapped the pixels to an X|Y grid (2D array or XY coords).

Now if the purpose is just to flatten an array, the most efficient way I am aware of would be to create a new 1D array the size of the total number of indices in the 2D array (RowMax * ColMax), and loop through the array.  I suppose these methods (above) would be particularly useful if you need to randomly or programmatically access indices in a non-linear fashion.

Anyways, just wanted to share a fun exercise with arrays.

Edited by spudw2k

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Chimp

$iY can also be calculated like this:

Local $iY = Int($iIndex / $iCol)

 

  • Like 1

small minds discuss people average minds discuss events great minds discuss ideas.... and use AutoIt....

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