[R] Using split and sapply to return entire lines

[Gabor Grothendieck]

Using package doBy at http://genetics.agrsci.dk/~sorenh/misc/index.html
try this:

summaryBy(cbind(length, ratio, monthly1, monthly2) ~ month, DF, max)



On 11/8/05, Todd A. Gibson <tgibson at augustcouncil.com> wrote:
> Hello,
> I have a data manipulation problem that I can easily resolve by using
> perl or python to pre-process the data, but I would prefer to do it
> directly in R.
>
> Given, for example:
>
>  month length ratio monthly1 monthly2
> 1 Jan   23     0.1   9        6
> 2 Jan   45     0.2   9        6
> 3 Jan   16     0.3   9        6
> 4 Feb   14     0.2   1        9
> 5 Mar   98     0.4   2        2
> 6 Mar   02     0.6   2        2
>
> (FWIW, monthly1 and monthly2 are unchanged for each month)
>
> I understand how to do aggregations on single fields using split and
> sapply, but how can I get entire lines.  For example, For the maximum
> of data$length grouped by data$month I would like to get back some
> form of:
>
> 2 Jan 45 0.2 9 6
> 4 Feb 14 0.2 1 9
> 5 Mar 98 0.4 2 2
>
> For mean, I would like to average all columns:
>
> Jan 28 0.2 9 6
> Feb 14 0.2 1 9
> Mar 50 0.5 2 2
>
> Thank you,
> -TAG
> Todd A. Gibson
>
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