[R] The equivalent of which() when accessing slots in an object

[William Dunlap]

vapply(buylist, slot, "reqstock", FUN.VALUE=0.0)
is closer in spirit than sapply() to purrr::map_dbl() - FUN.VALUE
gives the expected type and size of f's output.  vapply() is usually
quicker than sapply(), uses less memory, gives the right results
when given a vector of length 0, and gives an error when FUN does
not return the specified sort of result.


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Mon, Oct 31, 2016 at 7:31 AM, Bob Rudis <bob at rud.is> wrote:

>     which(purrr::map_dbl(buylist, slot, "reqstock") > 100)
>
> or
>
>     which(sapply(buylist, slot, "reqstock") > 100)
>
> ought to do the trick.
>
> On Mon, Oct 31, 2016 at 10:09 AM, Thomas Chesney
> <Thomas.Chesney at nottingham.ac.uk> wrote:
> > I have the following object
> >
> > setClass("buyer",
> > representation(
> > reqstock="numeric",
> > buyout="numeric"),
> > )
> >
> > nBuy <- 5
> >
> > #Set buyer parameters here
> > buylist <- list()
> > for (i in 1:nBuy){
> > buylist[[i]] <- new("buyer")
> > buylist[[i]]@reqstock <- sample(c(50:200),1)
> > }
> >
> > and want to count the number of objects in buylist that have reqstock
> greater than 100. Something like this if it was a vector:
> >
> > length(which(buylist[[]]@reqstock > 100))
> >
> > How could I do this please and where could I find more information about
> manipulating slots? When I try to search for this I just keep finding info
> on ls() and similar functions.
> >
> > Thank you
> >
> > Thomas Chesney
> > http://www.nottingham.ac.uk/~liztc/Personal/index.html
> >
> >
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