[R] MApply and SubStr

[Brian Trautman]

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 <dwinsemius at 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]]
> >
> > ______________________________________________
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> > 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
>
>

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