# [R] for() loop

David Freedman 3.14david at gmail.com
Mon Mar 15 12:20:47 CET 2010

```Hi - do you want

sum(datjan\$V4)
OR
sum(unique(datjan\$V4))  ?

there's also a cumsum function that might be useful

hth,
David Freedman, Atlanta

Schmidt Martin 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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