[R] why Vectorize conjures a list, not a vector?

[Jeff Newmiller]

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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Sent from my phone. Please excuse my brevity.

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"
>
>
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>
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