Re: [libreoffice-users] Re: Filter algorithm question

At 19:15 22/02/2015 -0700, Nobody Noname wrote:
> If I had a known irregular shape I could map it onto the existing 
> grid. A brute force approach would be to just make a list of all the 
> X-Y coordinates in the irregular area, then just search through the 
> entire grid and see if any coordinates show up in the list, and 
> count them if they do.

I think you are making work for yourself by suggesting doing this 
backwards. Don't create a list of cells in the shape and look to see 
if each contains a bird. Instead, use the defined boundary of the 
shape to determine directly whether each potential bird is in the 
shape. You need only one list - of birds. You don't need a list of 
cells that appear in the shape, just some way of determining whether 
any bird is inside it. Once you have the edges of the shape defined 
in some way, constructing a COUNTIF() condition to apply to the list 
of birds will give you what you need. Kidneys don't usually have 
holes (mine don't; I trust yours don't), so you probably need only a 
list of (two) limiting Y co-ordinates for each X value - or vice 
versa if this is easier.

> Creating this kind of pre-defined list with a grid that had a lot of 
> coordinates would be tougher as it would need to be done programmatically.

But you don't need this list: all you need is those co-ordinates (of 
the shape) in order to determine whether any bird in inside. How you 
get this depends on how your shape is defined (which you have not explained).

At 20:04 22/02/2015 -0700, Nobody Noname wrote:
> the algorithm I'm looking for is called "Flood Fill" ...

I really don't think it is - if your problem is as originally 
explained. If you want to colour in your imaginary diagram, by all 
mean use this. But once you have the definition of the shape (as you 
would need if you wanted to use flood fill), you can easily determine 
the status of each bird directly.

Brian Barker  


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