replacing ugly for loops
I am not sure you have expressed what you wanjt to do correctly. See inline:
On Wed, Oct 10, 2012 at 9:10 PM, andrewH <ahoerner at rprogress.org> wrote:
I have a couple of hundred American Community Survey Summary Files files containing rectangular arrays of data, mainly though not exclusively numeric. Each file is referred to as a sequence (henceforth "seq").
-- so 1 "seq" (terrible identifier -- see below for why) = 1 file From
these files I am trying to extract particular subsets (tables) consisting of a sets of columns. These tables are defined by three numbers (now in columns in a data frame): 1. a file identifier (seq) 2. first column position numbers (startNo) 3. length of table (len)
So your data frame, call it yourframe, has columns named: seq startNo len
so the columns to select for one triple would consist of startNo:(startNo+length-1). I am trying to create for each sequence a vector of all the column numbers for tables in that sequence.
So for each seq id you want to find all the column numbers, right? sq.n <- seq_len(nrow(yourframe)) ## Just to make it easier to read colms <- tapply(sq.n, yourframe$seq,function(x) with(yourframe[x,], sort(unique(do.call(c, mapply(seq, from=startNo, length=len,SIMPLIFY = FALSE))))) ## Comments In the mapply call, seq is the R function, ?seq. That's why using it as a name for a file id is terrible -- it causes confusion. In the absence of data, this is untested -- and probably not quite right. But it should be close, I hope. The key idea is the use of mapply to get the sequence of columns for each row in all the rows for each seq id. The SIMPLIFY = FALSE guarantees that this yields a list of vectors of column indices, which are then glopped together and cleaned up by the sort(unique(do.call( ... stuff. colms should then be a list giving the sorted column numbers to choose for each "seq" id. I do not know whether (once cleaned up,) this is either more elegant or more efficient than what you proposed. And I wouldn't be surprised if someone like Bill Dunlap comes up with a lot better way, either. But it is different -- and perhaps amusing. ... If I have properly understood what you wanted. If not, ignore all. Cheers, Bert
Obviously I could do this with nested for loops,e.g..
seq <- c(1,1,2,2)
startNo <- c(3, 10, 3, 15)
len <- c(4, 2, 5, 3)
data.df <- data.frame(seq, startNo, len)
seq.f <- factor(data.df$seq)
data.l <- split(data.df, seq.f)
selectColsList<- vector("list", length(levels(seq.f)))
for (i in seq_along(levels(seq.f))){
selectCols <- numeric()
for (j in seq_along(data.l[[i]]$startNo)){
selectCols <- c(selectCols,
data.l[[i]]$startNo[j]:(data.l[[i]]$startNo[j]
data.l[[i]]$len[j]-1))
}
selectColsList[[i]] <- selectCols
}
selectColsList
[[1]] [1] 3 4 5 6 10 11 [[2]] [1] 3 4 5 6 7 15 16 17 But this code strikes me as inelegant and verbose. It seems to me that there ought to be a way to make the outer loop, (indexed with i) into a tapply function (which is why I started with a split()), and the inner loop (indexed with j) into some cute recursive function, but I was not able to do so. If anyone could suggest some nicer (e.g. shorter, or faster, or just more sophisticated) way to do this instead, I would be most grateful. Sincerely, andrewH -- View this message in context: http://r.789695.n4.nabble.com/replacing-ugly-for-loops-tp4645821.html Sent from the R help mailing list archive at Nabble.com.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
Bert Gunter Genentech Nonclinical Biostatistics Internal Contact Info: Phone: 467-7374 Website: http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm