[R] Subset() within function: logical error

[Rich Shepard]

On Tue, 30 Jun 2015, Rolf Turner wrote:

> If you want a pointer to the correct syntax for subset(), try 
> help("subset")!!!
>
> The syntax of your "extstream" function is totally screwed up, convoluted and 
> over-complicated. Note that even if you had your "subset" argument specified 
> correctly, the return() call will give you only the result from the *first* 
> pass through the for loop.
>
> That aside, the error message is perfectly clear: 'subset' must be logical. 
> Your "subset" argument is "stream" which is a factor.
>
> You *could* redefine your "extstream" function as follows:
>
> function(alldf) {
>    sname <- levels(alldf$stream)
>    rslt <- vector("list",length(sname))
>    names(rslt) <- sname
>    for (i in sname) {
>       rslt[[i]] <- subset(alldf, alldf$stream==i, sampdate:quant)
>    }
>    rslt
> }
>
> However you don't need to go through such contortions:
>
>    split(testset,testset$stream)
>
> will give essentially what you want.  If you wish to strip out the redundant 
> "stream" column from the data frames in the resulting list, you could do that 
> using lapply()

Rolf,

   I did re-read the subset man page, but did not associate the error message
with the problem.

   Thanks very much for the lesson. I will read the split() man page; simple
is always better.

Regards,

Rich