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

[Ivan Calandra]

Thanks Ivan for the answer.

So it confirms my first thought that these two functions are equivalent
when applied to a "simple" data.frame.

The reason I was asking is because I have gotten used to use length() in
my scripts. It works perfectly and I understand it easily. But to be
honest, ncol() is more intuitive to most users (especially the novice)
so I was thinking about switching to using this function instead (all my
data.frames are created from read.csv() or similar functions so there
should not be any issue). But before doing that, I want to be sure that
it is not going to create unexpected results.

Thank you,
Ivan

--
Dr. Ivan Calandra
TraCEr, laboratory for Traceology and Controlled Experiments
MONREPOS Archaeological Research Centre and
Museum for Human Behavioural Evolution
Schloss Monrepos
56567 Neuwied, Germany
+49 (0) 2631 9772-243
https://www.researchgate.net/profile/Ivan_Calandra

On 31/03/2020 16:00, Ivan Krylov wrote:
> 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))
> dim(x)
> # [1] 87  1
> length(x)
> # [1] 1
> dim(x[,1])
> # [1] 87 61
>
>