The manual seems to suggest, with the SIMPLIFY = TRUE default option,
Vectorize would conjure a vector if possible.
Quote:
SIMPLIFY: logical or character string; attempt to reduce the result to
a vector, matrix or higher dimensional array; see the
?simplify? argument of ?sapply?.
I assume, if each run of the function results a vector of the same type,
the result should be a vector as well; there is a need of list only when
data are of different type.
Or, given vectors of the same type, conjure vectors of the same type.
But it doesn't work that way -- see below -- so what's the magic inside?
REPRODUCE:
First, to make sure each run of the function always return vector of the
same time:
> for (datafile in list.files(full.names=TRUE,"16b"))
print(mode(list.files(full.names=TRUE,datafile)))
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
[1] "character"
Then, vectorize it:
> datafiles <- c(Vectorize(list.files,
"path")(full.names=TRUE,path = list.files(base_dir,full.names=TRUE)))
> mode(datafiles)
[1] "list"
The same happened with sapply, which should generate list only if a vector
is impossible -- it generated a list when every result is a vector:
> mode(sapply(list.files(base_dir,full.names=TRUE), list.files))
[1] "list"
Vectorize is a functional version of a for loop that maps scalars to vectors or
uniform length vectors to matrices, or any non-uniform vector to a list. Type
the name of the function to see how it is implemented. You are giving it vectors
of a variety of lengths, so you are getting a list back. You can call unlist on
the result to flatten the list if that is what you want. In this case it seems
overkill...
list.files(pattern="\\.csv$",recursive=TRUE,full.names=TRUE) seems
more practical.
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Zhang Weiwu <zhangweiwu at realss.com> wrote:>
>The manual seems to suggest, with the SIMPLIFY = TRUE default option,
>Vectorize would conjure a vector if possible.
>
>Quote:
>
> SIMPLIFY: logical or character string; attempt to reduce the result to
> a vector, matrix or higher dimensional array; see the
> ?simplify? argument of ?sapply?.
>
>I assume, if each run of the function results a vector of the same
>type,
>the result should be a vector as well; there is a need of list only
>when
>data are of different type.
>
>Or, given vectors of the same type, conjure vectors of the same type.
>
>But it doesn't work that way -- see below -- so what's the magic
>inside?
>
>REPRODUCE:
>
>First, to make sure each run of the function always return vector of
>the
>same time:
>
>> for (datafile in list.files(full.names=TRUE,"16b"))
>print(mode(list.files(full.names=TRUE,datafile)))
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>[1] "character"
>
>
>Then, vectorize it:
>
>> datafiles <- c(Vectorize(list.files,
"path")(full.names=TRUE,path
>list.files(base_dir,full.names=TRUE)))
>> mode(datafiles)
>[1] "list"
>
>The same happened with sapply, which should generate list only if a
>vector
>is impossible -- it generated a list when every result is a vector:
>
>> mode(sapply(list.files(base_dir,full.names=TRUE), list.files))
>[1] "list"
>
>
>------------------------------------------------------------------------
>
>______________________________________________
>R-help at r-project.org mailing list
>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.
Hi Zhang, First note that a list is a vector (try is.vector(list())). The documentation for sapply() and Vectorize() should say *atomic* vector instead of vector in the desccription of the 'simplify' and 'SIMPLIFY' arguments. So in order for sapply() to be able to simplify the result, all runs of the function not only need to produce an atomic vector of the same type, but also of the same length. If this common length is 1, then the final result can be simplified to an atomic vector of the same length as the input. HTH, H. On 08/14/2013 08:01 PM, Zhang Weiwu wrote:> > The manual seems to suggest, with the SIMPLIFY = TRUE default option, > Vectorize would conjure a vector if possible. > > Quote: > > SIMPLIFY: logical or character string; attempt to reduce the result to > a vector, matrix or higher dimensional array; see the > ?simplify? argument of ?sapply?. > > I assume, if each run of the function results a vector of the same type, > the result should be a vector as well; there is a need of list only when > data are of different type. > > Or, given vectors of the same type, conjure vectors of the same type. > > But it doesn't work that way -- see below -- so what's the magic inside? > > REPRODUCE: > > First, to make sure each run of the function always return vector of the > same time: > >> for (datafile in list.files(full.names=TRUE,"16b")) >> print(mode(list.files(full.names=TRUE,datafile))) > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > [1] "character" > > > Then, vectorize it: > >> datafiles <- c(Vectorize(list.files, "path")(full.names=TRUE,path >> list.files(base_dir,full.names=TRUE))) >> mode(datafiles) > [1] "list" > > The same happened with sapply, which should generate list only if a > vector is impossible -- it generated a list when every result is a vector: > >> mode(sapply(list.files(base_dir,full.names=TRUE), list.files)) > [1] "list" > > > ______________________________________________ > R-help at r-project.org mailing list > 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. >-- Herv? Pag?s Program in Computational Biology Division of Public Health Sciences Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N, M1-B514 P.O. Box 19024 Seattle, WA 98109-1024 E-mail: hpages at fhcrc.org Phone: (206) 667-5791 Fax: (206) 667-1319