[R] summary tables with tapply

[Stefanie von Felten, IPW&IfU]

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