Erlang list comprehension, traversing two lists and excluding values

Posted by ErJab on Stack Overflow See other posts from Stack Overflow or by ErJab
Published on 2010-03-13T04:35:19Z Indexed on 2010/03/13 4:37 UTC
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erlang

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list-comprehension

I need to generate a set of coordinates in Erlang. Given one coordinate, say (x,y) I need to generate (x-1, y-1), (x-1, y), (x-1, y+1), (x, y-1), (x, y+1), (x+1, y-1), (x+1, y), (x+1, y+1). Basically all surrounding coordinates EXCEPT the middle coordinate (x,y). To generate all the nine coordinates, I do this currently:

[{X,Y} || X<-lists:seq(X-1,X+1), Y<-lists:seq(Y-1,Y+1)]

But this generates all the values, including (X,Y). How do I exclude (X,Y) from the list using filters in the list comprehension?

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