[R] by group

[PIKAL Petr]

Hi

Although you got several answers, simple aggregate was omitted.

> with(dat, aggregate(wt, list(Year=Year, Sex=Sex), mean))
  Year Sex        x
1 2001   F 12.00000
2 2002   F 13.33333
3 2003   F 12.00000
4 2001   M 15.00000
5 2002   M 16.33333
6 2003   M 15.00000

you can reshape the result 
> library(reshape2)
Warning message:
package 'reshape2' was built under R version 4.0.4 
> dcast(res, Year~Sex)
Using x as value column: use value.var to override.
  Year        F        M
1 2001 12.00000 15.00000
2 2002 13.33333 16.33333
3 2003 12.00000 15.00000

Cheers
Petr

> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Val
> Sent: Monday, November 1, 2021 10:08 PM
> To: r-help using R-project.org (r-help using r-project.org) <r-help using r-project.org>
> Subject: [R] by group
> 
> Hi All,
> 
> How can I generate mean by group. The sample data looks like as follow,
> dat<-read.table(text="Year Sex wt
> 2001 M 15
> 2001 M 14
> 2001 M 16
> 2001 F 12
> 2001 F 11
> 2001 F 13
> 2002 M 14
> 2002 M 18
> 2002 M 17
> 2002 F 11
> 2002 F 15
> 2002 F 14
> 2003 M 18
> 2003 M 13
> 2003 M 14
> 2003 F 15
> 2003 F 10
> 2003 F 11  ",header=TRUE)
> 
> The desired  output  is,
>              M        F
> 2001    15        12
> 2002    16.33   13.33
> 2003    15          12
> 
> Thank you,
> 
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