ncol() vs. length() on data.frames

Hi Ivan,

On 3/31/20 06:44, Ivan Calandra wrote:

That's exactly why I was asking if it really is equivalent and if there
are issues using one function or the other

Not that I know. It's mostly a matter of taste and code readability.

Either use the 2D interface:

?? ncol(df), colnames(df), df[ , "somecol"], cbind(), etc...

or the list interface:

?? length(df), names(df), df[["somecol"]], c(), etc...

to operate on your data.frames. They're equivalent. One advantage of
using the latter though is that your code would also work on list
objects that are not data.frames. But maybe you don't need or care
about that in which case using one interface or the other makes no
difference.

Note that the 2D interface is richer because it has nrow(),
rownames(), rbind() that are not part of the list interface.

From a code readability point of view I think one should be consistent
and avoid mixing the 2 styles. For example IMO using length(df) and
colnames(df) in the same function body is not good style. Either use
length(df) and names(df), or use ncol(df) and colnames(df). If in the
same function body you need to also access the rownames() then it
would make sense to stick to the 2D interface throughout the entire
body of your function.

Cheers,
H.

-- 
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
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On 31/03/2020 15:39, Eric Berger wrote:

Yes it does because?length(list) gives you the number of elements of
the list. And in the case of a data frame object that is the number of
columns, or ncol().

On Tue, Mar 31, 2020 at 4:37 PM Ivan Calandra <calandra at rgzm.de
<mailto:calandra at rgzm.de>> wrote:

???? Thanks Eric,

???? I know that, but that doesn't really answer my question, does it?

???? 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://urldefense.proofpoint.com/v2/url?u=https-3A__www.researchgate.net_profile_Ivan-5FCalandra&d=DwIDaQ&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=yZXfRqVdJeNf73bgLhzIctzOWowNX-0ccnNHdReiprw&s=rSFaISqU4VRbZBhLtnKvwJmxwkKQ0kAN0sIAfSBWUkw&e=

???? On 31/03/2020 15:26, Eric Berger wrote:
???? > A data frame is a special case of a list. It is a list of its
???? columns.
???? >
???? > > is.list( your_data_frame )
???? >
???? > # TRUE
???? >
???? >
???? > On Tue, Mar 31, 2020 at 4:04 PM Ivan Calandra <calandra at rgzm.de
???? <mailto:calandra at rgzm.de>
???? > <mailto:calandra at rgzm.de <mailto:calandra at rgzm.de>>> wrote:
???? >
???? >? ? ?Dear useRs,
???? >
???? >? ? ?I have a very simple question:
???? >? ? ?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?
???? >? ? ?Is one of them to be preferred for whatever reason?
???? >
???? >? ? ?Thanks 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://urldefense.proofpoint.com/v2/url?u=https-3A__www.researchgate.net_profile_Ivan-5FCalandra&d=DwIDaQ&c=eRAMFD45gAfqt84VtBcfhQ&r=BK7q3XeAvimeWdGbWY_wJYbW0WYiZvSXAJJKaaPhzWA&m=yZXfRqVdJeNf73bgLhzIctzOWowNX-0ccnNHdReiprw&s=rSFaISqU4VRbZBhLtnKvwJmxwkKQ0kAN0sIAfSBWUkw&e=
???? >
???? >? ? ?______________________________________________
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