[R] ncol() vs. length() on data.frames

Ivan Krylov kry|ov@r00t @end|ng |rom gm@||@com
Tue Mar 31 16:00:09 CEST 2020

On Tue, 31 Mar 2020 14:47:54 +0200
Ivan Calandra <calandra using rgzm.de> wrote:

> On a simple data.frame (i.e. each element is a vector), ncol() and
> length() will give the same result.

> Are they just equivalent on such objects, or are they differences in
> some cases?

I am not aware of any exceptions to ncol(dataframe)==length(dataframe)
(in fact, ncol(x) is dim(x)[2L] and ?dim says that dim(dataframe)
returns c(length(attr(dataframe, 'row.names')), length(dataframe))), but
watch out for AsIs columns which can have columns of their own:

x <- data.frame(I(volcano))
# [1] 87  1
# [1] 1
# [1] 87 61

Best regards,

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