[R] summary tables with tapply

[Uwe Ligges]

Stefanie von Felten, IPW&IfU 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?


I guess you want
   sapply(community, "[", 1)

Uwe Ligges


> Thanks for any suggestions!
> 
> Steffi
> 
>