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.4...@gmail.com>
Sent: Monday, November 1, 2021 8:50 PM
To: Val <valkr...@gmail.com>
Cc: Avi Gross <avigr...@verizon.net>; r-help mailing list <r-help@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 <valkr...@gmail.com
<mailto:valkr...@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@r-project.org <mailto:r-help@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-boun...@r-project.org
> <mailto:r-help-boun...@r-project.org> > On Behalf Of Jim Lemon
> Sent: Monday, November 1, 2021 6:25 PM
> To: Val <valkr...@gmail.com <mailto:valkr...@gmail.com> >; r-help mailing
> list <r-help@r-project.org <mailto:r-help@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 <valkr...@gmail.com
> <mailto:valkr...@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@r-project.org <mailto:R-help@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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> UNSUBSCRIBE and more, see
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>
> ______________________________________________
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