[R] Help me get this function to work...

[David Winsemius]

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
West Hartford, CT