1) I have this grid
x <- rep(c(1:8),c(rep(6,8))) y <- rep(c(1:6),8)
I need to make some others grids with same length and different numbers of points whit a random spatial pattern.
This is a bit imprecise. What do you mean by 'same length and different numbers of points'?
Your grid above has 8*6 = 42 points. Do you want to generate a random subset of these grid points, selecting each point with a fixed probability, or selecting exactly N points?
Firstly, I would make your grid above using 'expand.grid':
fullGrid <- expand.grid(1:8,1:6) plot(fullGrid)
Then you can use the sample() function to choose 10 different integers from 1 to 42, and use that to choose rows of the fullGrid data frame:
thinGrid <- fullGrid[sample(42,10),] plot(thinGrid)
This gives you exactly 10 points.
Or you could choose each point with some probability, using runif(42) to generate uniform random numbers and compare this with a threshold:
thin2 <- fullGrid[runif(42)>.8,] plot(thin2)
This gives grids with differing numbers of points, but each of the 42 points has a 0.2 probability of being included.
2) I need to produce some grids with the same numbers of points in different degrees of aggregation, the level of aggregation for all grids must be statistically different.
How to do these grids in R and how to test the significance between these grids?
I think at this point you need to find a good textbook on spatial point processes, then come back and look at R packages spatstat and to a lesser extent, splancs.
Hope this helps,
Baz
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