[R] Apply a function according to factor levels.

[Rui Barradas]

Hello,

Or ?aggregate, depending on the wanted output. With the dataset provided 
by the op, apply function mean.

dat <- read.table(text="
  values ind sample
1  0.03325   1      1
2  0.03305   1      1
3  0.03185   1      1
[...etc...]
44 0.03060   5      4
45 0.06605   5      5
", header = TRUE)

tapply(dat$values, dat$sample, mean)  # named vector
        1        2        3        4        5
0.033556 0.011120 0.017750 0.030220 0.062060

aggregate(values ~ sample, data = dat, mean)  # data.frame
   sample   values
1      1 0.033556
2      2 0.011120
3      3 0.017750
4      4 0.030220
5      5 0.062060

Hope this helps,

Rui Barradas

Em 17-08-2012 02:41, David L Carlson escreveu:
> ?tapply
>
> ----------------------------------------------
> David L Carlson
> Associate Professor of Anthropology
> Texas A&M University
> College Station, TX 77843-4352
>
>
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> project.org] On Behalf Of li li
>> Sent: Thursday, August 16, 2012 8:31 PM
>> To: r-help
>> Subject: [R] Apply a function according to factor levels.
>>
>> Dear all,
>>     I have a question on applying a function to the data according to
>> factor
>> levels.
>> For example, for the data below, what is the best way to apply a
>> function
>> to
>> "values" according to different levels of "samples" (1,2,3,4,5)?
>>      values ind sample
>> 1  0.03325   1      1
>> 2  0.03305   1      1
>> 3  0.03185   1      1
>> 4  0.03515   1      1
>> 5  0.03375   1      1
>> 6  0.01180   1      2
>> 7  0.01850   1      3
>> 8  0.02915   1      4
>> 9  0.06200   1      5
>> 10 0.03230   2      1
>> 11 0.03345   2      1
>> 12 0.03385   2      1
>> 13 0.03605   2      1
>> 14 0.03225   2      1
>> 15 0.01145   2      2
>> 16 0.01805   2      3
>> 17 0.02950   2      4
>> 18 0.05995   2      5
>> 19 0.03425   3      1
>> 20 0.03575   3      1
>> 21 0.03535   3      1
>> 22 0.03380   3      1
>> 23 0.03410   3      1
>> 24 0.01050   3      2
>> 25 0.01735   3      3
>> 26 0.03140   3      4
>> 27 0.06170   3      5
>> 28 0.03430   4      1
>> 29 0.03185   4      1
>> 30 0.03165   4      1
>> 31 0.03380   4      1
>> 32 0.03235   4      1
>> 33 0.01100   4      2
>> 34 0.01825   4      3
>> 35 0.03045   4      4
>> 36 0.06060   4      5
>> 37 0.03280   5      1
>> 38 0.03350   5      1
>> 39 0.03215   5      1
>> 40 0.03545   5      1
>> 41 0.03285   5      1
>> 42 0.01085   5      2
>> 43 0.01660   5      3
>> 44 0.03060   5      4
>> 45 0.06605   5      5
>>
>>
>>     Thank you.
>>        Hannah
>>
>> 	[[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-
>> guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.