search for: m199

I need some help summarizing complex data frames (small example below): m1_1 m2_1 m3_1 m1_2 m2_2 m3_2 i1 1 1 1 2 2 2 i1 2 1 1 2 2 2 i2 2 2 1 2 2 2 For an arbitrary number of columns (say m1 ?. m199) where the column names have variable patterns, and such that each set of columns is repeated (with potentially unique data) an arbitrary number of times (say _1 ? _1000), I would like to summarize by row the mean values of (m1, m2, m3, ? m199) over all replicates (_1, _2, _3, ? _1000). I need t...