Dear list,
Here's a little problem I already solved with my own coding style, but I feel there is a more efficient and cleaner way to write it, but had no success finding the "clever" solution.
I want to produce a factor from a subset of the combination of two vectors. I have the vectors a et b in a data-frame :
> df <- expand.grid(a=c(0, 5, 10, 25, 50), b=c(0, 25, 50, 100, 200)) > fac.df a b 1 0 0 2 5 0 3 10 0 4 25 0 5 50 0 6 0 25 7 5 25 <snip>
and want to create a factor which levels correspond to particular combinations of a and b (let's say Low for a=0 & b=0, Medium for a=10 & b=50, High for a=50 & b=200, others levels set to NA), reading them from a data-frame which describes the desired subset and corresponding levels.
Here's my own solution (inputs are data-frames df and cas, output is the sub factor):
> cas <- as.data.frame(matrix(c(0, 10,50, 0, 50, 200), 3, 2,dimnames=list(c("Low", "Medium", "High"), c("a", "b"))))
> cas
a b
Low 0 0
Medium 10 50
High 50 200
> sub <- character(length(df$a))
> for (i in 1:length(df$a)) {
+ temp <- rownames(cas)[cas$a==df$a[i] & cas$b==df$b[i]]
+ sub[i] <- ifelse(length(temp)>0, temp, NA)
+ }
> sub <- ordered(sub, levels=c("Low", "Medium", "High"))
> sub
[1] Low <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> Medium <NA> <NA> <NA> <NA> [18] <NA> <NA> <NA> <NA> <NA> <NA> <NA> High Levels: Low < Medium < High
I was looking for a vectorized solution (apply style) binding data-frames df and cas, but didn't succeed avoiding the for loop. Could anybody bring me the ligths over the darkness of my ignorance ? Thank you very much in advance.
-- Ir. Yves BROSTAUX Unit� de Statistique et Informatique Facult� universitaire des Sciences agronomiques de Gembloux (FUSAGx) 8, avenue de la Facult� B-5030 Gembloux Belgique T�l: +32 81 62 24 69 Email: [EMAIL PROTECTED]
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