> Dear list,
> I have a data frame like:
>
> > log2.ratios[1:3,1:4]
>            ID                  a1             a2             a3
> 1 GS1-232B23      -0.0207500 0.17553833  0.21939333
> 2 RP11-82D16      -0.1896667 0.02645167 -0.03112333
> 3 RP11-62M23      -0.1761700 0.08214500 -0.04877000
> 4 RP11-62M23      0.2761700 -0.15214500 -0.05877000
>

the 3rd and 4th rows are of the same ID, I would like to take the avarage of
these
two rows and get the data frame to:

        ID                  a1             a2             a3
1 GS1-232B23      -0.0207500 0.17553833  0.21939333
2 RP11-82D16      -0.1896667 0.02645167 -0.03112333
3 RP11-62M23      -0.05         -0.035           0.094135

Can anyone suggest how to deal with this (to take the ave of two rows of the
same ID ) more quickly?

Thanks a bunch!

Allen

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