Hi Daniel, Thanks for the reply, that was the one missing piece! I had been trying to use the tapply() function, but was getting an error message about unequal length until now.
I wrote: VAL_mean_xpart <- tapply(X[ ,2], PARTF, mean) and got the column 2 means by factors just as I had hoped. One more question: how could I make an expression that would automatically perform this operation for all columns 2 through ncol? I tried: VAL_mean_xpart <- tapply(X[ ,*2:n*], PARTF, mean) and VAL_mean_xpart <- tapply(X[ ,*2:ncol(X)*], PARTF, mean) but obviously I was just unsure of how to specify "each column in the data frame". Thanks again for your help! Best, Logan On Sat, Oct 15, 2011 at 2:22 PM, Daniel Malter [via R] < ml-node+s789695n3908298...@n4.nabble.com> wrote: > You access columns of a data.frame by column indices as in: X[ ,1], X[ ,2], > etc. The index before the comma would stand for the row if you wanted to > restrict those. The index after the comma captures the column. > > That said, you typically would not "extract" rows from the data frame but > draw directly from the data frame for an analysis contingent on the factors > in column 1. You may want to look at the tapply() function, in particular. > > HTH, > Daniel > > jawbonemurphy wrote: > Hi, > > I converted an Excel file into a .txt file "X.txt" with no header > (X.txt<http://r.789695.n4.nabble.com/file/n3908157/X.txt>) > and imported it with: > > X <- read.table("/Users/johnlogandurland/Desktop/X.txt", header=FALSE). > > What I would like to do is to make the first column into a factors vector, > and then analyze the rest of the columns in the data table using those > factors. The problem is, I haven't found a way to convert the rest of the > columns into vectors with length = nrows so I can apply the factors vector > to them. > > When I try: > > vect <- X[1] > > I get an object with class "data.frame" and length 1, and the "[[]]" > command seems to turn the column into a "factor" vector, though with the > right length. This seems like it should be a really easy thing to do, but > I've looked through R-intro and been unable to find a good answer. Any > ideas? > > Many Thanks, > Logan > > > > ------------------------------ > If you reply to this email, your message will be added to the discussion > below: > > http://r.789695.n4.nabble.com/Turning-Data-Frame-Columns-into-Vectors-tp3908157p3908298.html > To unsubscribe from Turning Data Frame Columns into Vectors, click > here<http://r.789695.n4.nabble.com/template/NamlServlet.jtp?macro=unsubscribe_by_code&node=3908157&code=amR1cmxhbmRzdGVyQGdtYWlsLmNvbXwzOTA4MTU3fDE4NTIyMTcxNzk=>. > > -- View this message in context: http://r.789695.n4.nabble.com/Turning-Data-Frame-Columns-into-Vectors-tp3908157p3908393.html Sent from the R help mailing list archive at Nabble.com. [[alternative HTML version deleted]] ______________________________________________ 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.
