[R] summary tables with tapply

[Gabor Grothendieck]

I am not sure I understand the question but is the situation that
you have two vectors: x and y such that for each level of y
x is constant so that for each level of y you want to find that value
of x?  In that case:

x <- c("A", "A", "A", "B", "B")
y <- c(1,1,2,3,3)
unique(data.frame(x,y))

or

tapply(x, y, head, 1)

or

tapply(x, y, "[", 1)

or if x is a factor
xf <- factor(x)
tapply(as.character(xf), y, head, 1)


Aside. I suggest you use dput to display your data in your post to
make it easier for
others to read it back into R, e.g.

> dput(x)
c("A", "A", "A", "B", "B")

and editing that allows one to post this:

x <- c("A", "A", "A", "B", "B")


On 3/11/06, Stefanie von Felten, IPW&IfU <sfelten at uwinst.unizh.ch> wrote:
> Hello everyone,
>
> #I have a long table with a factor Plotfac:
>  > Plotfac[1:20]
>   [1] 1   1   1   1   2   2   2   2   3   3   3   3   4   4   4   4   5
>   5   6   6
>
> #there is the species diversity of each plot (Plotfac):
> DataSort$div[1:20]
>  [1] 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 2 2 2 2
>
> #and the plant community growing in each plot:
>  > DataSort$community[1:20]
>  [1] DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1
> DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  DLRT_1  ARR HOL
> [18] ARR HOL ARR HOL ARR HOL
>
> #Now I want to have a summary table with data on the plotlevel
> #I define the new plot variable:
> Newplot<-levels(Plotfac)#a vector with all plotnumbers 1-n)
>  >Newplot[1:10]
> [1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "15" "16"
>
> #the new div variable (div is numeric, so mean is no problem)
> PlotDiv<-tapply(DataSort$div,Plotfac,mean)
>  > PlotDiv[1:10]
>  1  2  3  4  5  6  7  8 15 16
>  4  4  4  4  2  2  2  2  2  2
>
> #BUT HOW CAN I DO THIS WITH THE CHARACTER COMMUNITY?
> #A rather unsatisfactory solution:
> community<-tapply(DataSort$community,Plotfac,as.character)
> results in:
> community[1:5]
> $"1"
> [1] "DLRT_1" "DLRT_1" "DLRT_1" "DLRT_1"
>
> $"2"
> [1] "DLRT_1" "DLRT_1" "DLRT_1" "DLRT_1"
>
> $"3"
> [1] "DLRT_1" "DLRT_1" "DLRT_1" "DLRT_1"
>
> $"4"
> [1] "DLRT_1" "DLRT_1" "DLRT_1" "DLRT_1"
>
> $"5"
> [1] "ARR HOL" "ARR HOL"
> #how can I make community look like
> "DLRT_1", DLRT_1","DLRT_1","DLRT_1","ARR HOL"...
> #without repeating the community of each observation within a plot? Is
> it possible to extract a single "value" out of these repeated structures?
>
> Thanks for any suggestions!
>
> Steffi
>
>
> --
> ---------------------------------
> Stefanie von Felten
> Doktorandin
>
> ETH Zürich
> Institut für Pflanzenwissenschaften
> ETH Zentrum, LFW A 2
>
> Telefon: 044 632 85 97
> Telefax: 044 632 11 53
> e-mail:  stefanie.vonfelten at ipw.agrl.ethz.ch
> http://www.ipw.agrl.ethz.ch/~svfelten/
>
> und:
>
> Universität Zürich
> Institut für Umweltwissenschaften
> Winterthurerstrasse 190
> 8057 Zürich
>
> Telefon: 044 635 61 23
> Telefax: 044 635 57 11
> e-mail:  sfelten at uwinst.unizh.ch
> http://www.unizh.ch/uwinst/homepages/steffi.html
>
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