[R] where does the null come from?

Wacek Kusnierczyk Waclaw.Marcin.Kusnierczyk at idi.ntnu.no
Wed May 13 11:55:00 CEST 2009

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.


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