Hi,
I usually use aggregate() for this:
aggregate(datjan,list(datjan[,4]),sum)
with the advantage that you can use any other aggregation function (mean,
var and so on...). See help.
Miguel
On Sun, Mar 14, 2010 at 8:49 PM, Schmidt Martin <m.schm...@students.unibe.ch
> wrote:
> Hello
>
> I'm working with R since a few month and have still many trivial questions
> - I guess! Here is what I want:
>
> I have this matrix:
>
>> dim(datjan)
>>
> [1] 899 4
>
> The first 10 rows looks as follows:
>
>> datjan[1:10,]
>>
> V1 V2 V3 V4
> 1 1961 1 1 24
> 2 1961 1 2 24
> 3 1961 1 3 24
> 4 1961 1 4 24
> 5 1961 1 5 24
> 6 1961 1 6 27
> 7 1961 1 7 27
> 8 1961 1 8 27
> 9 1961 1 9 27
> 10 1961 1 10 27
>
> I tried now to create a for() loop, which gives me the sum of the 30
> different classes (1:30!) in [,4].
>
> for(i in 1:30){
> sum(datjan[,4]==i)
> }
>
> R is then actually calculating the sum of "i" which certainly doesn't exist
> and results in a "0" value
>
> t1<-sum(datjan[,4]==1)
> t2<-sum(datjan[,4]==2)
> .................................until '30'
> This way its working, but I won't find a end by doing all this by hand,
> because there are many other matrix waiting.
>
> So, how can I make work that loop??
>
> thanks for helping me
>
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