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

[Luigi Marongiu]

Thank you, the last is exactly what I was looking for.

On Tue, Oct 24, 2023 at 2:41 PM 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.
> >
> > ______________________________________________
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> > and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Sarah Goslee (she/her)
> http://www.numberwright.com



-- 
Best regards,
Luigi