Steven Kang schrieb:
Dear R users,
I would like to accumulate objects generated from 'for' loop to a list or
array.
To illustrate the problem, arbitrary data set and script is shown below,
x <- data.frame(a = c(rep("n",3),rep("y",2),rep("n",3),rep("y",2)), b =
c(rep("y",2),rep("n",4),rep("y",3),"n"), c = c(rep("n",7),rep("y",3)), d =
c("y", rep("n",4), rep("y",2), rep("n",3)))
for (i in 1:(dim(x)[2])) {
assign(paste("ind", i, sep = ""), which(x[ , i] == "y"))
accum <- c(ind1, ind2, ind3, ind4)
}
Using "for" loops is not idiomatic; I tend to use them only if I really
need intermediate results.
res <- apply(x, 2, function(answer) which(answer == "y"))
names(res) <- paste("ind", 1:ncol(x), sep="")
ind1
[1] 4 5 9 10
ind2
[1] 1 2 7 8 9
ind3
[1] 8 9 10
ind4
[1] 1 6 7
accum
[1] 4 5 9 10 1 2 7 8 9 8 9 10 1 6 7
Are there any alternative method where the highlighted statement above can
be represented without typing individual objects manually? (as it can be
very tedious with large number of objects; i.e ind1, ind2, ....., ind100)
/I think you are looking for unlist()./
Also, is there any way to extract individual objects ('ind1' etc) from
'accum'?
Well, I think they are not objects by themselves anymore. You may want
to give the vector elements individual names based on their origin and
then extract appropriate elements by string matching.
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