[R] Calculating means in a new table Dear all - I imported (on a Mac) a big table with >2000 lines: > mydata <- read.table(file("/Users/didiw/Desktop/R/all.txt"), header = TRUE)  > mydata[1:15,]    location Spezies Spec E.MPa.   Phi No Trial   1        LC       P    J  13.27  7.51  1     1   2        LC       P    J  14.24  6.68  1     1   3        LC       P    J  14.28  7.01  2     1   4        LC       P    J  16.65  6.30  1     2   .... Now i want to crate a new table "mymeans" where all means and Stdev  of E.MPa and Phi when location, Spezies, No, and Trial are the same,  something like this:    location Spezies Spec No Trial mean.E	stddev.E	mean.Phi	std.Phi 1        LC       P    J 1     1  xx		xx		xx		xx 2        LC       P    J 2     1  xx		xx		xx		xx   3        LC       P    J 1     2  xx		xx		xx		xx      .... Because I we did ca 8 repetition of each measurement, the new table should have only 2000/8 lines. Thanks for any help! -didi ______________________________________________ R-help@stat.math.ethz.ch 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.