Check the result of sapply(logical(0), all) !
?On 8/12/20, 12:33 PM, "Bioc-devel on behalf of Laurent Gatto" <bioc-devel-bounces at r-project.org on behalf of laurent.gatto at uclouvain.be> wrote:
Dear all,
I have a quick question regarding the usage of vapply and sapply. The former is recommended to insure that the output is always a vector of a specific type. For example:
> df1 <- data.frame(x = 1:3, y = LETTERS[1:3]) ## OK test
> df2 <- data.frame(x = 1:3, y = Sys.time() + 1:3) ## Not OK test
> sapply(df1, class) ## vector of chars, OK
x y
"integer" "character"
> sapply(df2, class) ## ouch, not a vector
$x
[1] "integer"
$y
[1] "POSIXct" "POSIXt"
> vapply(df2, class, character(1)) ## prefer an error rather than a list
Error in vapply(df2, class, character(1)) : values must be length 1,
but FUN(X[[2]]) result is length 2
There are cases, however, were FUN ensures that the output will be of length 1 and of a expected type. For example
- sapply(X, all) - all() always returns logical(1)
- sapply(X, length) - always numeric(1) (integer(1) or double(1) for vectors of more than 2^31 - 1 elements)
or more generally
- sapply(X, slot, "myslot") - slot() will always return a character(1) because @myslot is always character(1) (as defined by the class)
Would you still recommend to use vapply() in such cases?
Thank you in advance.
Laurent
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