[R] behavior of "by"

[Jeff Laake]

Thanks to those that replied.  It was reproducible on my system but it 
was nested within other code which would have been obvious had I left 
the browse> portions in it.  The reason for the behavior was obvious 
when I used str(samples).  Even though Effort looked like a vector in 
samples, it was actually an array [,1:10] which was created from a 
tapply.  I was unaware that a dataframe could contain an array.  Learned 
something new. Next time I'll make sure my reproducible code is not 
nested.  Interesting difference between tapply and by behavior in that case.
 

Sebastian P. Luque wrote:
> On Tue, 28 Oct 2008 18:04:57 -0700,
> Jeff Laake <Jeff.Laake at noaa.gov> wrote:
>
>   
>> Any insight into the behavior of "by" in the following case would be
>> appreciated.  There is a note in the help details for "by" about
>> documenting behavior since v2.7 but I don't entirely understand what
>> it is saying.  I'm using R2.7.2 Windows.  I'm interested if the
>> following behavior was a change or whether it has always worked this
>> way.  I looked at RSiteSearch and read through version changes but
>> found nothing.
>>     
>
>   
>> Take a dataframe as follows:
>>     
>>> samples
>>>       
>>   Region.Label Area Sample.Label Effort Label 1 1 10000 1 100 11 2 1
>> 10000 2 100 12 3 1 10000 3 100 13 4 1 10000 4 100 14 5 1 10000 5 100
>> 15 6 1 10000 6 100 16 7 1 10000 7 100 17 8 1 10000 8 100 18 9 1 10000
>> 9 100 19 10 1 10000 10 100 110
>>     
>
> I cannot reproduce your results (please provide reproducible code), but:
>
> table(samples$Region.Label)
>
> is simpler for this purpose.
>
>
>