Umberto Maggiore wrote:
I cannot figure out how, using R, I can paste indexes or characters to the variable
names which are used within loops. I will explain this with a simple example:
Immagine I have a huge series of variables, each one taken two times, say
x1 x2 y1 y2 z1 z2.....
Now, immagine that I want to compute a variable from the difference of
each couple, say dx=x1-x2, dy=y1-y2, dz=z1-z2...
In Stata, for example, this wold be straightforward:
foreach i in x y z {
gen d`i'= `i'1-`i'2
}
With R I tried to use paste( ) but I found that it applies to objects,
not to variable names.
best regards,
Umberto
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Try: x1<-10 x2<-20 y1<-5 y2<-22 z1<-4 z2<-7 for(i in c("x","y","z")){ eval(parse(text=paste("d",i,"<-",i,"1 - ",i,"2",sep=""))) } ls(pattern="d")
output-start Wed Sep 22 14:38:28 2004 [1] "dx" "dy" "dz" output-end
but why don't you store x1,y1,z1 and x2,y2,z2 in a list:
a<-list(x=1:4, y=1:7, z=1:5) b<-list(x=(1:4)*10, y=1:7, z=(1:5)-20) d<-sapply(1:3, function(i) a[[i]]-b[[i]] )
@ output-start Wed Sep 22 14:43:09 2004 [[1]] [1] -9 -18 -27 -36 [[2]] [1] 0 0 0 0 0 0 0 [[3]] [1] 20 20 20 20 20 output-end
Peter Wolf
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