Hi All:
I'm looking to find out a bit more about how subassignment actually works and
am hoping someone with knowledge of the details can fill me in (I've looked at
the source code, but my knowledge of C is lacking).
In the case of vectors, my reading of ?"[" would indicate that for a vector,
vec <- 1:25, vec[c(1,5,25)] <- c(101,102,103)is functionally the same as
indx <- c(1,5,25) for (i in 1:length(indx)) vec[indx[i]] <- c(101,102,103)[i]
And in the case of a data frame, df <- data.frame(d1=1:10,d2=11:20,d3=21:30),
df[c(1,5,10),c(1,3)] <- data.frame(a=101:103,b=104:106)is functionally the
same as rowindx <- c(1,5,10) colindx <- c(1,3) for (i in
1:length(rowindx)) { for (j in 1:length(colindx))
df[rowindx[i],colindx[j]] <- data.frame(a=101:103,b=104:106)[i,j] }
Obviously I've verified that these examples work and I realize that my loops
also contain subassignments; what I'm really after is to understand the
mechanics of replacing multiple elements. Is a for-loop the proper way to
understand the sequential nature of subassignments here (even if it is not
actually implemented using a loop)?
Cheers,HR
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