Searching a matrix for values "surrounding" it

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SudoCode
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Posts: 61
Joined: Fri May 04, 2012 7:05 pm

Searching a matrix for values "surrounding" it

Post by SudoCode » Sun Sep 30, 2012 4:51 pm

So I have a 100x100 matrix, created by

Code: Select all

function newNodeMap(tableName, numRows, numColumns)
  for i = 1, numRows do
    tableName[i] = {}
    for j = 1, numColumns do
      tableName[i][j] = 0
    end
  end
end
Which is then populated with values from 0-2 by tile properties from Advanced Tiled Loader. The problem now is that I need a way to read specific values of the matrix if given one index. i.e. [i+1], [i-1]. [j+1], [j-1], [i+1][j-1], etc.

I googled a bit but essentially everything I found was for matlab and I'm not familiar with the syntax.
Last edited by SudoCode on Sun Sep 30, 2012 5:48 pm, edited 1 time in total.

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dreadkillz
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Posts: 223
Joined: Sun Mar 04, 2012 2:04 pm
Location: USA

Re: Searching a matrix for values "surrounding" it

Post by dreadkillz » Sun Sep 30, 2012 5:01 pm

Could you rephrase your question? Do you mean you want to get the surrounding 8 values in a matrix if you're given an index?

Kinda like this?

[x][x][x]
[x][x]
[x][x][x]

SudoCode
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Posts: 61
Joined: Fri May 04, 2012 7:05 pm

Re: Searching a matrix for values "surrounding" it

Post by SudoCode » Sun Sep 30, 2012 5:47 pm

Yes, index, not value, my mistake :P

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Inny
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Location: New York

Re: Searching a matrix for values "surrounding" it

Post by Inny » Sun Sep 30, 2012 6:26 pm

I'm going to interpret this as you've given a location, say (50, 50) and need to check (49, 49) through (51, 51) for something. This is easily done with a few pieces of code:

Use this function to safely get values from the matrix:

Code: Select all

function getFromNodeMap(tableName, row, column)
  local row = tableName[row]
  if type(row)=="nil" then return 0 end -- Or some terminal value that's acceptable
  local value = tableName[column]
  if type(value)=="nil" then return 0 end -- Or some terminal value that's acceptable
  return value
end
Now, it's safe to pull the 8 surrounding values:

Code: Select all

function getValuesAround(tableName, row, column)
  local values = {}
  for y = row-1, row+1 do
    for x = column-1, column+1 do
      if y~=row and x~=column then
        values[#values+1] = getFromNodeMap(tableName, y, x)
      end
    end
  end
  return values
end

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