R help - Jul 2009 - Help me get this function to work...

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 
            }
        }
}


Cover.fn("VFFF1-7")

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M_WL_QA_HM_celebrity_photos2_072009&cat=celebrity

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")
>
> _________________________________________________________________
>
> right from Hotmail. Check it out.
>
> M_WL_QA_HM_celebrity_photos2_072009&cat=celebrity
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT

On Mon, Jul 13, 2009 at 12:08 PM, David Winsemius<dwinsemius at
comcast.net> wrote:
> 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.
>
>
<SNIP>
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
How important it is to wrap the list in a return statement, ala

return(list(ShrubCover.df, TreeCover.df, TotalCover.df))

or

answer <- list(ShrubCover.df, TreeCover.df, TotalCover.df)
return(answer)

Thanks,
Mark