That's exactly what I wanted, thank you very much!
My intent was to perform the SubStr operation first, and then apply the
types to the columns. I wasn't expecting the two types in the same column.
I appreciate your response!
On Tue, Feb 10, 2015 at 5:03 PM, David Winsemius <dwinsem...@comcast.net>
wrote:
>
> On Feb 10, 2015, at 3:58 PM, Brian Trautman wrote:
>
> > Hi!
> >
> > I'm trying to write a custom function that applies SubStr to a string,
> and
> > then depending on the arguments, converts the output to a number.
> >
> > The substring part of my code works fine, but it's not converting the
> way I
> > want to --
> >
> > options('stringsAsFactors'=FALSE)
> > require(data.table)
> >
> > substr_typeswitch <- function(x, start, stop, typeto='chr')
> > {
> > tmpvar <- substr(x=x, start=start, stop=stop)
> > tmpvar <- switch(typeto, num=as.numeric(tmpvar), tmpvar)
> > return(tmpvar)
> > }
> > startpos <- c(01, 03)
> > endpos <- c(02, 04)
> > typelist <- c('chr', 'num')
> >
> > startdata <- as.data.table(c('aa01', 'bb02'))
> >
> > enddata_want <- as.data.table(mapply(substr_typeswitch, startdata,
> > startpos, endpos, typelist))
> >
> > If I examine enddata_want --
> >
> >> str(enddata_want)
> > Classes ‘data.table’ and 'data.frame': 2 obs. of 2 variables:
> > $ V1: chr "aa" "bb"
> > $ NA: chr "1" "2"
> > - attr(*, ".internal.selfref")=<externalptr>
> >
> > "1" and "2" are being stored as character, and not as number.
>
> It appears from you code that you might be expecting a vector in a
> dataframe object to have a character mode in the first postition and a
> numeric mode in the second position. That wouldn't seem to be a reasonable
> expectation. But maybe you were hoping the chr and num types were to be
> applied to columns. I was surprised to get something different from
> as.data.table:
>
> > str(enddata_want)
> Classes ‘data.table’ and 'data.frame': 2 obs. of 2 variables:
> $ V1: Factor w/ 2 levels "aa","bb": 1 2
> $ NA: Factor w/ 2 levels "1","2": 1 2
> - attr(*, ".internal.selfref")=<externalptr>
>
> The mapply operation made a matrix which forces all values to be the same
> mode:
>
> > str( mapply(substr_typeswitch, startdata,
> + startpos, endpos, typelist) )
> chr [1:2, 1:2] "aa" "bb" "1" "2"
> - attr(*, "dimnames")=List of 2
> ..$ : NULL
> ..$ : chr [1:2] "V1" NA
>
> You might have gotten something less homogeneous if you added the SIMPLIFY
> argument:
>
> > str( mapply(substr_typeswitch, startdata,
> + startpos, endpos, typelist, SIMPLIFY=FALSE) )
> List of 2
> $ V1: chr [1:2] "aa" "bb"
> $ NA: num [1:2] 1 2
>
>
>
>
> >
> > Can anyone help me understand what I'm doing wrong?
> >
> > Thank you!
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> > 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
> Alameda, CA, USA
>
>
[[alternative HTML version deleted]]
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