[R] averaging pairs of columns in a dataframe

[Gabor Grothendieck]

Try this:

# test data
DF <- data.frame(a = 1:9, a = 21:29, b = 31:39, b = 41:49, check.names = FALSE)

t(apply(DF, 1, tapply, names(DF), mean))

It gives a matrix so use as.data.frame on that if you need a data frame

On Wed, Aug 27, 2008 at 9:47 AM, JonD <jonathan.denniss at googlemail.com> wrote:
>
> Dear all,
>
> I have a dataframe with 132 columns and 100 rows.  Every 2nd column is a
> repeat measurement so that the columns could be titled, a a b b c c d d etc.
> I would like to average the repeats such that I am left with a data frame of
> 66 columns (of means) and 100 rows.
>
> I have been trying to use rowMeans but have not been able to average the
> pairs of columns, only the whole dataframe.
>
> Any help would be appreciated, I am new to R.
>
> Thanks in advance,
>
> Jon.
> --
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