I don't think it is good general advice to suggest that people use
`subset()` in a function. You have to be every so clever to make this work
right once you call `foo()` inside another function because of where
`eval(cond)` is doing its evaluation of the `condition` won't be the same
as when you call `foo()` at the top level. There's a reason for the Warning
section in `?subset`.

G


On 6 June 2014 13:48, Sargeant, Glen <gsargeant@usgs.gov> wrote:

> As you are trying to learning to write functions, I'll submit a very
> general solution
> that illustrates a couple of core skills.  It returns a random sample of
> rows for
> any dataframe and any condition, and accepts optional arguments to
> "sample."
>
> #Example data
> Idf1 <- c(12,14,15,16,17,18,19,21,25,24,26,28,29,32,33,35,36,37,48)
> casod <- c(1,1,1,1,3,3,3,3,1,1,1,1,3,3,3,1,3,1,3)
> mydatabase <- data.frame(Idf1,casod)
>
> #Required arguments are `df', a dataframe, and `condition',
> #a character string.  The function also accepts  optional
> #arguments to `sample'
>
> foo <- function(df,condition,...){
>   cond <- parse(text=condition)
>   df. <- subset(df,eval(cond))
>   idx <- sample(1:nrow(df.),...)
>   df.[idx,])
> }
>
> foo(df=mydatabase,condition="casod!=1",size=5,replace=FALSE)
> foo(df=mydatabase,condition="casod!=1",size=10,replace=TRUE)
>
>
>
>
>
>
>
>
> On Fri, Jun 6, 2014 at 8:39 AM, Rodrigues <rodriguesmsb@gmail.com> wrote:
>
> > Dear R users,
> >
> >
> > I’m trying to build a function to select random samples idf’s from a
> > database.
> > So, my data frame had 2 columns and 575 rows. Follow bellow an example of
> > my
> > database
> > Idf1    casod
> > 12      1
> > 14      1
> > 15      1
> > 16      1
> > 17      3
> > 18      3
> > 19      3
> > 21      3
> > 25      1
> > 24      1
> > 26      1
> > 28      1
> > 29      3
> > 32      3
> > 33      3
> > 35      1
> > 36      3
> > 37      1
> > 48      3
> >
> > So my function is
> >
> > blinding=function(sample){
> >   sort=sample(idf1,10,replace=F)
> >   return(sort2)
> > }
> >
> > It is pretty simple and I would like to add one more step in my choice. I
> > would like to link my choice to casod stats. Thus if casod==3 sample
> would
> > be random idfs could not be an idf with casod=1. Does someone can help
> me?
> >
> >
> >
> >
> > --
> > View this message in context:
> >
> http://r-sig-ecology.471788.n2.nabble.com/Help-with-a-function-tp7578931.html
> > Sent from the r-sig-ecology mailing list archive at Nabble.com.
> >
> > _______________________________________________
> > R-sig-ecology mailing list
> > R-sig-ecology@r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
> >
>
>
>
> --
> Glen Sargeant, Ph.D.
> Research Wildlife Biologist/Statistician
> USGS Northern Prairie Wildlife Research Center
> E-mail: gsargeant@usgs.gov
> Phone: (701) 253-5528
>
>         [[alternative HTML version deleted]]
>
>
> _______________________________________________
> R-sig-ecology mailing list
> R-sig-ecology@r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-ecology
>
>


-- 

Gavin Simpson, PhD

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