[R] Data

[David Winsemius]

On Dec 11, 2009, at 4:38 PM, Jose Narillos de Santos wrote:

> Hi all,
>
> Imagine I have a matrix and the first colum is a list that repeats  
> the same
> names, I want to sum the second column on each unique name on first  
> column.
>
> Imagine this:
>
> Pepe 2
> Pepe 3
> Pepe 4
> Jose 2
> Jose 5
> Manuel 4
> Manuel 2

?tapply    # or one of its derivative fucntions like by or aggregate
>
> I want to make a new matrix that calculates and recognizes that  
> there are 3
> different names ans sum second column. But a priori I don´t know the  
> list of
> the different names:
>
> In my example
Something like:

tapply(valuecol, namecol, sum)

(Untested.)

>
> Pepe 9
> Jose 7
> Manuel 6
>
> I´m trying to use something like sapply or apply but I can find the  
> key...
>
> Can anyone help or guide me ?
>
> Thanks in advance¡¡¡
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT