Hello,
Em 31-08-2012 11:35, Martin Maechler escreveu:> Hi Rui,
>
> I think when people are asking how to do such basic things in R,
> the answer should *not* be to use a (non-base / -recommended)
> package...
You're right, that's why I've called it an alternative.
>
> but then, you may have really wanted to advertize plyr,
> so never mind.
It' usefull to know that those extra *ply functions are available.
Anyway, my vote goes to Bill Dunlap's read.table solution. I would never
have thought of that one.
Rui Barradas>
> Martin
>
>>>>>> "RB" == Rui Barradas <ruipbarradas at
sapo.pt>
>>>>>> on Thu, 30 Aug 2012 18:57:34 +0100 writes:
> RB> Hello,
>
> RB> Yet another alternative.
>
>
> RB> library(plyr)
> RB> dfr <- ldply(strsplit(c("a,1", "b,2",
"c,3"), ","), identity)
> RB> str(dfr)
>
> RB> #dfr$V2 <- as.numeric(dfr$V2)
>
> RB> So, if the op was about conversion to df, the answer is yes.
>
> RB> Rui Barradas
>
> RB> Em 30-08-2012 18:14, David Winsemius escreveu:
> >>
> >> On Aug 30, 2012, at 9:44 AM, Sam Steingold wrote:
> >>
> >>>> * Sam Steingold <fqf at tah.bet> [2012-08-30
08:56:17 -0400]:
> >>>>
> >>>> Is there a way for an apply-type function to return a
data frame?
> >>>> the closest thing I think of is
> >>>>
> >>>> foo <- as.data.frame(t(sapply(...)))
> >>>> names(foo) <- c(....)
> >>>
> >>> alas, this has a problem of creating a
"homogeneous" data frame, i.e.,
> >>> all the columns are numbers or characters, because the
function passed
> >>> to sapply returns c(....) and
> >>>> c(1,2,"a")
> >>> [1] "1" "2" "a"
> >>>
> >>> e.g.,
> >>>
as.data.frame(t(sapply(c("a,1","b,2","c,3"),function
(n)
> >>> strsplit(n,",")[[1]])))
> >>> V1 V2
> >>> a,1 a 1
> >>> b,2 b 2
> >>> c,3 c 3
> >>>
> >>> 'data.frame': 3 obs. of 2 variables:
> >>> $ V1: Factor w/ 3 levels
"a","b","c": 1 2 3
> >>> ..- attr(*, "names")= chr "a,1"
"b,2" "c,3"
> >>> $ V2: Factor w/ 3 levels
"1","2","3": 1 2 3
> >>> ..- attr(*, "names")= chr "a,1"
"b,2" "c,3"
> >>>
> >>> I wanted the V1 column to be a string, and V2 to be a
number.
> >>> (I know stringsAsFactors=FALSE would replace factors with
strings, but I
> >>> need a string and a number)
> >>>
> >>> I could, of course, do ret$V2 <- as.numeric(ret$V2)
but this would mean
> >>> a double conversion: from number to string first (by c())
and then back.
> >>
> >> It is starting as a 'string' ('character' in
R parlance) so you will
> >> need to coerce it to "numeric" at some point:
> >>
> >> Consider this alternate route:
> >>
> >> > do.call(rbind,
strsplit(c("a,1","b,2","c,3"), ",") )
> >> [,1] [,2]
> >> [1,] "a" "1"
> >> [2,] "b" "2"
> >> [3,] "c" "3"
> >> > as.data.frame( do.call(rbind,
strsplit(c("a,1","b,2","c,3"), ",") ) )
> >> V1 V2
> >> 1 a 1
> >> 2 b 2
> >> 3 c 3
> >>
> >> > str( as.data.frame( do.call(rbind,
strsplit(c("a,1","b,2","c,3"),
> >> ",") ) , stringsAsFactors=FALSE) )
> >> 'data.frame': 3 obs. of 2 variables:
> >> $ V1: chr "a" "b" "c"
> >> $ V2: chr "1" "2" "3"
> >>
>
> RB> ______________________________________________
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