[R] Combining data replicates

[John Leamon]

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
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