In R a function only returns the last evaluation, so you need to wrap
up all of the local results into a list at the end of the function.
On Jul 13, 2009, at 1:23 PM, Chip Maney wrote:
I have a function (see below). This function has one object, ID.
If I run the loops by itself using a character value (ie,"VFFF1-7"),
then the loops work fine. However, when I try to insert the
character value via the function call, it doesn't work. I don't get
an error, but the TotalCover.df dataframe does not update according
to the loop criteria. Any obvious problems that you can see?
################Cover Function#########################
#Define Variables
Quadrats.df<-unique(data.df$Quadrat)
TotalCover.df<-cbind(0:750/10,0,0,0,0,0,0)
colnames(TotalCover.df)<-
c("Station","Shrub","Tree","Invasive","Herb","Litter","Bare")
Shrub.df<-data.df[data.df$Layer=="Shrub",]
Tree.df<-data.df[data.df$Layer=="Tree",]
Cover.fn<-function(ID){
ShrubCover.df<-Shrub.df[Shrub.df$Quadrat==ID,]
for (j in 1:length(ShrubCover.df[,"Quadrat"])){
for (i in 1:751){
if
(TotalCover.df[i,"Station"]>=ShrubCover.df[j,"Start"] &&
TotalCover.df[i,"Station"]<= ShrubCover.df[j,"Stop"])
TotalCover.df[i,"Shrub"]<- 1
}
}
TreeCover.df<-Tree.df[Tree.df$Quadrat==ID,]
for (j in 1:length(TreeCover.df[,"Quadrat"])){
for (i in 1:751){
if
(TotalCover.df[i,"Station"]>=TreeCover.df[j,"Start"] &&
TotalCover.df[i,"Station"]<= TreeCover.df[j,"Stop"])
TotalCover.df[i,"Tree"]<- 1
}
}
# Perhaps something like:
list(ShrubCover.df, TreeCover.df, TotalCover.df)
}
Cover.fn("VFFF1-7")
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David Winsemius, MD
Heritage Laboratories
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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.
