Whats the point of multidimensional arrays?

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Stormwire

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Posted: 3rd Jul 2013 22:50

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Is there anything that multidimensional arrays can do that 1d arrays cant?

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Matty H

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Posted: 3rd Jul 2013 23:01

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No, a single array can do anything a multidimensional array can do.

Although multidimensional arrays sometimes provide a better way of logically separating your data. For example, an 8x8 array could represent a chess board, you could have a single dimensional array of 64 but there would be extra work to retrieve any individual square(eg. 3 across and 4 up).

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Ancient Lady

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Posted: 3rd Jul 2013 23:01

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Probably not.

But using multi-dimensional arrays can be very useful.

A simple case would be using an array to some value for every box in a gridded display.

If you use two dimensions, you can access the point you want quickly (code wise): x = myarray[r][c]

If you use a one-dimensional array, you need to calculate the position (assuming zero based): x = myarray[r*mywidth+c]

Yes, that is exactly what happens behind the scenes in the compiled version. But it is not as clean looking from a code point of view.

Similarly, a three dimension array would let you directly access any 3D block of space in a defined space.

There are lots of other very good uses for multi-dimensioned arrays.

Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master

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Stormwire

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Posted: 4th Jul 2013 00:42

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Thanks @Matty H @Ancient Lady

Quote: "A simple case would be using an array to some value for every box in a gridded display."

Exactly what I was trying to do before I got confused. Here's the thing, if grid[x, y] equals one value and grid[int] is equal to one value also then how is that of any use? You always get just one value out. That might be a really stupid question lol

What I was originally thinking before everything became messy was to store the X and Y values of dots in an multiD array and then extract the values in a loop as I create the dots. I got everything working except the extraction part.

The thing that's doing my melon in is I can only store and extract X or Y not X and Y.

+ Code Snippet


Rem Sets up array for storing data. X is wrong

SetVirtualResolution(1024,768)

Dim grid[32, 791] as integer

Stepxy = 32
Count = 23
last  = 0
x = 0
y = 0

For t = 0 To 32

    grid[t,i] = x

    For i = last To count

        grid[t, i] = y
        Inc y, 32
        If y > 768 Then y = 0

    Next i

    Inc last, 23
    Inc count, 23

    Inc x, 32

Next t


Count = 23
last  = 0


For t = 0 To 32

    For i = last To count

        OpenToWrite(1, "griddata.txt", 1)
        WriteLine(1, "T = " + STR(t) + ", I = " + STR(i) + ", Grid = " + STR(grid[t, i]))
        CloseFile(1)

    Next i

    Inc last, 23
    Inc count, 23

Next t


Do

    Count = 23
    last  = 0

    For t = 0 To 32

        For i = last To count

            y = grid[t, i]
            Dot(t, y, 255)

        Next i

        Inc last, 23
        Inc count, 23

    Next t

Sync()
Loop

Function Dot(x, y, c)

    DrawLine( x, y, x, y, c, c, c )

EndFunction

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Marl

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Posted: 4th Jul 2013 00:56 Edited at: 4th Jul 2013 01:00

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I think you may be over-thinking it.

Generally when you store griddy stuff in a multiD array, you store the contents not the coordinates The coordinates get you to the contents as indexes in the array.

grid[x,y] = value

However if you have a lists of things and you want to store their coodinates in an array, the list is one thing so you would use a 1D array. To store several things in a 1D array you need a custom type;

+ Code Snippet

type myObjectType
  xpos
  ypos
  sprite
  etc.
endtype

dim MyObject[ maxObject ] as myObjectType

then you can use stuff like;

MyObject[ count ].xpos = thisX
MyObject[ count ].ypos = thisY

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Stormwire

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Posted: 4th Jul 2013 01:04

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Thanks Marl, Im gonna go the Type route, it seems simpler.

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Ancient Lady

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Posted: 4th Jul 2013 01:21 Edited at: 4th Jul 2013 01:36

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There is at least one problem with this code:

+ Code Snippet

For t = 0 To 32

    grid[t,i] = x

    For i = last To count

        grid[t, i] = y
        Inc y, 32
        If y > 768 Then y = 0

    Next i

    Inc last, 23
    Inc count, 23

    Inc x, 32

Next t

You are assigning a value "grid[t,i] = x" outside of the loop that you define 'i' in. The first iteration through the 'For t' loop will have 'i' at zero (first use of undefined variable in AppGameKit is always zero). After that it will be set to count + 1, the value it was at when the 'For i' loop finishes. And the first line in your 'For t' loop is wiping out that x value.

And I really don't understand what you are trying to do. If you are trying to store the y value in the grid, there is no need to slide the second index, your 'i', the way you are doing.

I do know that the DrawLine function does not draw a point if the start and stop positions are the same. This was discovered by someone else in some other thread.

Try this (it creates a grid of dots and the file has the correct values):

Rem Sets up array for storing data
rem set the display
SetVirtualResolution(1024,768)

rem a type to hold the position
type tXY
  x as float
  y as float
endtype

rem the array to hold the grid of positions
Dim grid[32,23] as tXY

rem set the initial x & y positions
x# = 0
y# = 0

For t = 0 To 32
    For i = 0 To 23
        rem store the values
        grid[t,i].x = x#
        grid[t,i].y = y#

rem update the y (using inc actually messes this up and it shouldn't)
        y# = y# + 32
        If y# > 768 Then y# = 0
    Next i

rem update the x (same issue with inc)
    x# = x# + 32
Next t

OpenToWrite(1, "griddata.txt", 0)
For t = 0 To 32
    For i = 0 To 23
 		x# = grid[t,i].x
		y# = grid[t,i].y
      WriteLine(1, "T = " + STR(t) + ", I = " + STR(i) + ", Grid = " + STR(x#) + " x " + STR(y#))
    Next i
Next t
CloseFile(1)

Do
	if GetPointerPressed() then end
    For t = 0 To 32
        For i = 0 To 23
				x# = grid[t,i].x
				y# = grid[t,i].y
            Dot(x#, y#, 255)
        Next i
    Next t

Sync()
Loop

Function Dot(x as float, y as float, c as integer)

DrawLine( x, y, x+1, y+1, c, c, c )

EndFunction

+ Code Snippet

Rem Sets up array for storing data
rem set the display
SetVirtualResolution(1024,768)

rem a type to hold the position
type tXY
  x as float
  y as float
endtype

rem the array to hold the grid of positions
Dim grid[32,23] as tXY

rem set the initial x & y positions
x# = 0
y# = 0

For t = 0 To 32
    For i = 0 To 23
        rem store the values
        grid[t,i].x = x#
        grid[t,i].y = y#

        rem update the y (using inc actually messes this up and it shouldn't)
        y# = y# + 32
        If y# > 768 Then y# = 0
    Next i

    rem update the x (same issue with inc)
    x# = x# + 32
Next t

OpenToWrite(1, "griddata.txt", 0)
For t = 0 To 32
    For i = 0 To 23
 		x# = grid[t,i].x
		y# = grid[t,i].y
      WriteLine(1, "T = " + STR(t) + ", I = " + STR(i) + ", Grid = " + STR(x#) + " x " + STR(y#))
    Next i
Next t
CloseFile(1)


Do
	if GetPointerPressed() then end
    For t = 0 To 32
        For i = 0 To 23
				x# = grid[t,i].x
				y# = grid[t,i].y
            Dot(x#, y#, 255)
        Next i
    Next t

Sync()
Loop

Function Dot(x as float, y as float, c as integer)

    DrawLine( x, y, x+1, y+1, c, c, c )

EndFunction

Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master

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Stormwire

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Posted: 4th Jul 2013 01:37 Edited at: 4th Jul 2013 01:48

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They must have fixed the DrawLine command. Im using the latest beta. Heres what I got when I fixed the x position.

Quote: "
You are assigning a value "grid[t,i] = x" outside of the loop that you define 'i' in.
"

Thanks for that. I think thats why I am getting the gap in the middle.

Edit

just seen your code. Thats very helpful thanks!

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