[R] where does the null come from?

[Wacek Kusnierczyk]

m = matrix(1:4, 2)

apply(m, 1, cat, '\n')
# 1 2
# 3 4
# NULL

why the null?

vQ

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[K. Elo]

Hi!

Wacek Kusnierczyk wrote:
> m = matrix(1:4, 2)
>
> apply(m, 1, cat, '\n')
> # 1 2
> # 3 4
> # NULL
>
> why the null?

Could it be the return value of 'cat'. See ?cat, where:

---snip ---
Value
None (invisible NULL).
---snip ---

Kind regrads,
Kimmo

[Peter Dalgaard]

Wacek Kusnierczyk wrote:
> m = matrix(1:4, 2)
>
> apply(m, 1, cat, '\n')
> # 1 2
> # 3 4
> # NULL
>
> why the null?

It comes from unlist()ing a list of NULLs, which in turn are the return
values of cat().

It is arguably a design-buglet not to return list(NULL, NULL), but the
internal logic is to unlist() unless the first element is.recursive (and
NULL is not) or the return values have different length() (and all are
zero). It _is_, however, in accordance with the documentation (see the
Value: section):

--
O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B
c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dal...@biostat.ku.dk) FAX: (+45) 35327907

[Wacek Kusnierczyk]

Peter Dalgaard wrote:
> Wacek Kusnierczyk wrote:
>
>> m = matrix(1:4, 2)
>>
>> apply(m, 1, cat, '\n')
>> # 1 2
>> # 3 4
>> # NULL
>>
>> why the null?
>>
>
> It comes from unlist()ing a list of NULLs, which in turn are the return
> values of cat().
>

yes; i'd think i'd get a list of nulls, but...

> It is arguably a design-buglet not to return list(NULL, NULL), but the
> internal logic is to unlist() unless the first element is.recursive (and
> NULL is not) or the return values have different length() (and all are
> zero). It _is_, however, in accordance with the documentation (see the
> Value: section):
>

... i agree the actual outcome is appropriately explained in the docs.
i don't think it has no merit, but it's a bit surprising at first.

thanks,
vQ

[Gabor Grothendieck]

> out <- apply(m, 1, cat, '\n')
1 3
2 4
> out
NULL

[Ted Harding]

On 13-May-09 14:43:17, Gabor Grothendieck wrote:
>> out <- apply(m, 1, cat, '\n')
> 1 3
> 2 4
>> out
> NULL

Or, more explicitly, from ?cat :

Value:
None (invisible 'NULL').

Ted.

> On Wed, May 13, 2009 at 5:23 AM, Wacek Kusnierczyk
> <Waclaw.Marci...@idi.ntnu.no> wrote:

>> _ _m = matrix(1:4, 2)
>>
>> _ _apply(m, 1, cat, '\n')
>> _ _# 1 2
>> _ _# 3 4
>> _ _# NULL

>>
>> why the null?
>>
>> vQ
>>
>> ______________________________________________
>> R-h...@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>
>
> ______________________________________________
> R-h...@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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E-Mail: (Ted Harding) <Ted.H...@manchester.ac.uk>
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Date: 13-May-09 Time: 15:56:04
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