[R] aggregate and the $ operator

[Joe Ceradini]

Does this do what you want?

aggregate(Nuclei ~ Slide, example, sum)

On Fri, Jan 22, 2016 at 12:20 PM, Ed Siefker <ebs15242 at gmail.com> wrote:

> Aggregate does the right thing with column names when passing it
> numerical coordinates.
> Given a dataframe like this:
>
>   Nuclei Positive Nuclei Slide
> 1    133              96    A1
> 2     96              70    A1
> 3     62              52    A2
> 4     60              50    A2
>
> I can call 'aggregate' like this:
>
> > aggregate(example[1], by=example[3], sum)
>   Slide Nuclei
> 1    A1    229
> 2    A2    122
>
> But that means I have to keep track of which column is which number.
> If I try it the
> easy way, it doesn't keep track of column names and it forces me to
> coerce the 'by'
> to a list.
>
> > aggregate(example$Nuclei, by=list(example$Slide), sum)
>   Group.1   x
> 1      A1 229
> 2      A2 122
>
> Is there a better way to do this?  Thanks
> -Ed
>
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-- 
Cooperative Fish and Wildlife Research Unit
Zoology and Physiology Dept.
University of Wyoming
JoeCeradini at gmail.com / 914.707.8506
wyocoopunit.org

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