Got it. Thanks so much.
   Hannah

2012/8/16 arun <smartpink111@yahoo.com>

> Hi,
> Try this:
> dat1<-read.table(text="
>  no.   values ind sample
> 1  0.03325  1      1
> 2  0.03305  1      1
> 3  0.03185  1      1
> 4  0.03515  1      1
>
> -------------------------
> -------------------------
> 42 0.01085  5      2
> 43 0.01660  5      3
> 44 0.03060  5      4
> 45 0.06605  5      5
> ",sep="",header=TRUE)
> dat2<-within(dat1,{sample<-as.factor(sample)})
> ddply(dat2,.(sample), function(x) mean(x$values))
> # sample       V1
> #1      1 0.033556
> #2      2 0.011120
> #3      3 0.017750
> #4      4 0.030220
> #5      5 0.062060
> A.K.
>
> ----- Original Message -----
> From: li li <hannah.hlx@gmail.com>
> To: r-help <r-help@r-project.org>
> Cc:
> Sent: Thursday, August 16, 2012 9:31 PM
> 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]]
>
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>
>

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