Using split and sapply to return entire lines

Also, one can use aggregate:

aggregate(DF[,-1], list(month = DF$month), max)
The issue here is that I need the row corresponding to the month with
the maximum length.  That is, aggregate(.) is returning both the
maximum month and maximum ratio for all rows with month=Jan.  I need
the single row in month=Jan which has the maximum length.

Thanks,
-TAG
On 11/8/05, Gabor Grothendieck <ggrothendieck at gmail.com> wrote:
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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Using split and sapply to return entire lines

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