Hello all I'm are dealing with a sizeable data set from microarray analysis, which contains anywhere from 4 to 8 replicate DNA spots dispersed throughout the entire data set. I would like to be able to apply functions (such as medians, log transformations, st dev, co. variance, etc) to each set of replicates, then store the output for subsequent analysis and graphing. I've tried using By (), but it produces a separate data frame for every subgroup, and I haven't found a way to channel the output into a single results dataframe. I looked into apply, but I'm unclear on how to apply subgrouping to the data. Does anyone have and advice on the best way for me to proceed? Thanks in advance. John Leamon -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._