Hi Jose,

Here is a suggestion using tapply():

R> x <- read.table(textConnection("Pepe 2
+ Pepe 3
+ Pepe 4
+ Jose 2
+ Jose 5
+ Manuel 4
+ Manuel 2"), header = FALSE)
R> closeAllConnections()
R> x
       V1 V2
1   Pepe  2
2   Pepe  3
3   Pepe  4
4   Jose  2
5   Jose  5
6 Manuel  4
7 Manuel  2
R>
R>
R> with(x, tapply(V2, V1, sum))
   Jose Manuel   Pepe
      7      6      9

HTH,
Jorge


On 12/11/2009 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
>
> 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
>
> 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¡¡¡
>
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>
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>
>
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