In order to distribute a certain amount of TRUE (=1) values, depending on raster layer's values, I would like to do something like this:
Let's say I have a 9x2 matrix looking like this:
Example <- matrix(c(0.8,0.6,0.5,0.3,0.2,0.4,0.9,0.7,
0.1,1,1,1,1,1,0,0,0,0),ncol=2)
> Example
[,1] [,2]
[1,] 0.8 1
[2,] 0.6 1
[3,] 0.5 1
[4,] 0.3 1
[5,] 0.2 1
[6,] 0.4 0
[7,] 0.9 0
[8,] 0.7 0
[9,] 0.1 0
Now I want to allocate the 1's from [,2] as a function of the highest values of [,1] without changing the order of [,1]. The result should look like this:
> Example
[,1] [,2]
[1,] 0.8 1
[2,] 0.6 1
[3,] 0.5 1
[4,] 0.3 0
[5,] 0.2 0
[6,] 0.4 0
[7,] 0.9 1
[8,] 0.7 1
[9,] 0.1 0
Is there any elegant way to do this. I could't find any function to solve this problem. As I want to convert [,2] to a raster layer using the raster package a raster-based solution would work for me as well.
You can find how many 1's you have by summing column 2. You can then find your relative threshold of column 1 by checking if it is higher or lower than that value.
how.many.ones <- sum(Example[, 2])
max.thresh <- sort(Example[, 1], decreasing=TRUE)[how.many.ones]
change.to.one <- Example[, 1] >= max.thresh
Example[, 2] <- ifelse(change.to.one, 1, 0)
Example
[,1] [,2]
[1,] 0.8 1
[2,] 0.6 1
[3,] 0.5 1
[4,] 0.3 0
[5,] 0.2 0
[6,] 0.4 0
[7,] 0.9 1
[8,] 0.7 1
[9,] 0.1 0
There is no tie-handling in this process.