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Hi, I'm stuck with a fairly basic re-ordering problem. I want to extract part of a matrix as a vector, and reorder it to match with an erratic sequence of x,y coordinates. Here's an example that shows what I want and how close I've got (but for some reason my mind just can't get the final step at the moment!): #Define a grid: xy100 <- expand.grid(1:10, 1:10) # Define a matrix