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 <ruipbarra...@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 <f...@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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RB> and provide commented, minimal, self-contained, reproducible code.
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