I answered the wrong question. Here is the code to find all the matches for each row:
n <- 20 set.seed(2) # create test dataframe x <- as.data.frame(matrix(sample(1:2,n*6, TRUE), nrow=n)) x x.col <- c(1,3,5) # match against all the other rows x.match1 <- apply(x[, x.col], 1, function(a){ .mat <- which(apply(x[, x.col], 1, function(z){ all(a == z) })) }) # remove matches to itself x.match2 <- lapply(seq(length(x.match1)), function(z){ x.match1[[z]][!(x.match1[[z]] %in% z)] }) # x.match2 contains which rows indices match On Wed, Oct 7, 2009 at 3:52 PM, Rama Ramakrishnan <r...@alum.mit.edu> wrote: > > Hi Friends, > > I have a data frame d. Let vars be the column indices for a subset of the > columns in d (e.g., vars <- c(1,3,4,8)) > > For each row r in d, I want to collect all the other rows in d that match > the values in row r for just the columns in vars. > > The naive way to do this is to have a for loop stepping through each row in > d, and within the loop have another loop going through all the rows again, > checking for equality. This is quadratic in the number of rows and takes way > too long. Is there a better, "vectorized" way to do this? > > Thanks in advance! > > Rama Ramakrishnan > > ______________________________________________ > R-help@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. > -- Jim Holtman Cincinnati, OH +1 513 646 9390 What is the problem that you are trying to solve? ______________________________________________ R-help@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.