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: brostaux.y at fsagx.ac.be