[R] by group

Tue Nov 2 02:04:28 CET 2021

That works, Bert. I do note the result, d, is a matrix and works because everything within it is numeric. I have no problem with that for this problem.

For a more general problem with a data.frame type of object with columns of any type, the proper output might better be a data.frame. Of course, in this case, the matric can easily be coerced back into a data.frame:

d <- as.data.frame(with(dat, tapply(wt, list(Year, Sex), mean)))

d

F        M

2001 12.00000 15.00000

2002 13.33333 16.33333

2003 12.00000 15.00000

str(d)

'data.frame':      3 obs. of  2 variables:

  $ F: num  12 13.3 12

$ M: num  15 16.3 15

From: Bert Gunter <bgunter.4567 using gmail.com> 
Sent: Monday, November 1, 2021 8:50 PM
To: Val <valkremk using gmail.com>
Cc: Avi Gross <avigross using verizon.net>; r-help mailing list <r-help using r-project.org>
Subject: Re: [R] by group

"A decent example was given and I see Andrew provided a base R reply that
should be sufficient. But I do not think he realized you wanted something
different so his answer is not in the format you wanted:"

Yes, but it is trivial to modify Andrew's suggestion to get almost exactly what Val has requested (one merely needs to read ?tapply carefully) without having to resort to tidyverse gymnastics:

> d <- with(dat, tapply(wt, list(Year, Sex), mean))
> d
            F        M
2001 12.00000 15.00000
2002 13.33333 16.33333
2003 12.00000 15.00000

This is a matrix, not a data.frame. write() or write.table()  can be used to write it to a file in whatever format is desired (e.g. with or without row,column names. Etc.

Cheers,

Bert

Bert Gunter

"The trouble with having an open mind is that people keep coming along and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Mon, Nov 1, 2021 at 4:44 PM Val <valkremk using gmail.com <mailto:valkremk using gmail.com> > wrote:

Thank you all!
I can assure you that this is not  HW. This is a sample of my large
data set and I want a simple  and efficient approach to get the
desired  output   in that particular format.  That file will be saved
and used  as an input file for another external process.

val

On Mon, Nov 1, 2021 at 6:08 PM Avi Gross via R-help
<r-help using r-project.org <mailto:r-help using r-project.org> > wrote:
>
> Jim,
>
> Your code gives the output in quite a different format and as an object of
> class "by" that is not easily convertible to a data.frame. So, yes, it is an
> answer that produces the right numbers but not in the places or data
> structures I think they (or if it is HW ...) wanted.
>
> Trivial standard cases are often handled by a single step but more complex
> ones often suggest a multi-part approach.
>
> Of course Val gets to decide what approach works best for them within
> whatever constraints we here are not made aware of. If this is a class
> assignment, it likely would be using only tools discussed in the class. So I
> would not suggest using a dplyr/tidyverse approach if that is not covered or
> even part of a class. If this is a project in the real world, it becomes a
> matter of programming taste and convenience and so on.
>
> Maybe Val can share more about the situation so we can see what is helpful
> and what is not. Realistically, I can think of way too many ways to get the
> required output.
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org <mailto:r-help-bounces using r-project.org> > On Behalf Of Jim Lemon
> Sent: Monday, November 1, 2021 6:25 PM
> To: Val <valkremk using gmail.com <mailto:valkremk using gmail.com> >; r-help mailing list <r-help using r-project.org <mailto:r-help using r-project.org> >
> Subject: Re: [R] by group
>
> Hi Val,
> I think you answered your own question:
>
> by(dat$wt,dat[,c("Sex","Year")],mean)
>
> Jim
>
> On Tue, Nov 2, 2021 at 8:09 AM Val <valkremk using gmail.com <mailto:valkremk using gmail.com> > wrote:
> >
> > 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,
> >
> > ______________________________________________
> > R-help using r-project.org <mailto: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.
>
> ______________________________________________
> R-help using r-project.org <mailto: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.
>
> ______________________________________________
> R-help using r-project.org <mailto: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.

______________________________________________
R-help using r-project.org <mailto: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.

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