On Tue, 3 Aug 2004, Jinsong Zhao wrote: > I hope to remove a whole column from a data frame or matrix (> 2000 > columns). All value in the column are same. The first thing is to > select those columns. > > For instance, I hope to remove the V3~6 column, for all the value in > those colume is zero. > > V3 V4 V5 V6 V7 V8 V9 V10 > 1 0 0 0 0 0.000 0.000 0.000 0.000 > 2 0 0 0 0 0.000 0.000 0.000 0.000 > 3 0 0 0 0 0.000 0.000 0.000 0.000 > 4 0 0 0 0 0.000 0.000 0.000 0.000 > 5 0 0 0 0 0.000 0.000 0.000 0.000 > 6 0 0 0 0 -0.001 -0.001 -0.001 -0.001 > 7 0 0 0 0 0.000 0.000 0.000 -0.001 > 8 0 0 0 0 0.000 0.000 0.000 -0.001 > 9 0 0 0 0 -0.009 -0.012 -0.015 -0.018 > > I mean how to select the first four columns.
mydf2 <- mydf[-(1:4)] If you wanted to remove all columns which were entirely zero, you could use cols <- sapply(mydf, function(x) all(x == 0)) mydf2 <- mydf[!cols] > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html which suggests you read `An Introduction to R', and that covers this and more. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html