[R] How to Calculate the Mean by Multiple Groups in R

[peter dalgaard]

Also,

> aggregate(cbind(OD, ODnorm) ~ Time + Target + Conc, data = df, FUN = "mean")
  Time Target Conc       OD    ODnorm
1    1   BACT    1 765.3333 108.33333
2    1   BACT    2 745.3333  88.33333
3    1   BACT    3 675.0000  18.00000

(You might wish for "cbind(OD,ODnorm) ~ . - Well", but aggregate.formula is not smart enough for that.)

-pd

> On 24 Oct 2023, at 14:40 , Sarah Goslee <sarah.goslee using gmail.com> wrote:
> 
> Hi,
> 
> I think you're misunderstanding which set of variables go on either
> side of the formula.
> 
> Is this what you're looking for?
> 
>> aggregate(OD ~ Time + Target + Conc, data = df, FUN = "mean")
>  Time Target Conc       OD
> 1    1   BACT    1 765.3333
> 2    1   BACT    2 745.3333
> 3    1   BACT    3 675.0000
>> aggregate(ODnorm ~ Time + Target + Conc, data = df, FUN = "mean")
>  Time Target Conc    ODnorm
> 1    1   BACT    1 108.33333
> 2    1   BACT    2  88.33333
> 3    1   BACT    3  18.00000
> 
> Or using a different form, that might be more straightforward to you:
> 
>> aggregate(df[, c("OD", "ODnorm")], by = df[, c("Time", "Target", "Conc")], data = df, FUN = "mean")
>  Time Target Conc       OD    ODnorm
> 1    1   BACT    1 765.3333 108.33333
> 2    1   BACT    2 745.3333  88.33333
> 3    1   BACT    3 675.0000  18.00000
> 
> Sarah
> 
> On Tue, Oct 24, 2023 at 8:31 AM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>> 
>> Hello,
>> I have a data frame with different groups (Time, Target, Conc) and
>> each entry has a triplicate value of the measurements OD and ODnorm.
>> How can I merge the triplicates into a single mean value?
>> I tried the following:
>> ```
>> df = data.frame(Time=rep(1, 9), Well=paste("A", 1:9, sep=""),
>>                OD=c(666, 815, 815, 702, 739, 795, 657, 705, 663),
>>                Target=rep("BACT", 9),
>>                Conc=c(1,1,1,2,2,2,3,3,3),
>>                ODnorm=c(9, 158, 158,  45,  82, 138,   0,  48,   6),
>>                stringsAsFactors = FALSE)
>> aggregate(.~ODnorm, df, mean)
>> 
>>> aggregate(.~ODnorm, df, mean)
>>  ODnorm Time Well OD Target Conc
>> 1      0   NA   NA NA     NA   NA
>> 2      6   NA   NA NA     NA   NA
>> 3      9   NA   NA NA     NA   NA
>> 4     45   NA   NA NA     NA   NA
>> 5     48   NA   NA NA     NA   NA
>> 6     82   NA   NA NA     NA   NA
>> 7    138   NA   NA NA     NA   NA
>> 8    158   NA   NA NA     NA   NA
>> 
>> aggregate(cbind(Time, Target, Conc) ~ ODnorm, df, mean)
>>  ODnorm Time Target Conc
>> 1      0   NA     NA   NA
>> 2      6   NA     NA   NA
>> 3      9   NA     NA   NA
>> 4     45   NA     NA   NA
>> 5     48   NA     NA   NA
>> 6     82   NA     NA   NA
>> 7    138   NA     NA   NA
>> 8    158   NA     NA   NA
>> ```
>> 
>> Thank you.
>> 
>> ______________________________________________
>> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
> 
> 
> 
> -- 
> Sarah Goslee (she/her)
> http://www.numberwright.com
> 
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> 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.

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
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