R help - Jan 2008 - R loops

I'm a new user and am having trouble with loops.
In the following, I'm trying to add the results of "test" and the
loops are
not working.
I've simplified the loop.  What am I doing wrong?
Thanks!
> test<-numeric(20)
> tot<-numeric(20)
> for(i in 1:20){test[i]<-1}
> for (i in 1:20){tot[i]<-(test[i]+tot[i])}
> tot
 [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

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On 1/28/2008 8:48 AM, cvandy wrote:
> I'm a new user and am having trouble with loops.
> In the following, I'm trying to add the results of "test" and
the loops are
> not working.
> I've simplified the loop.  What am I doing wrong?
> Thanks!
>> test<-numeric(20)
>> tot<-numeric(20)
>> for(i in 1:20){test[i]<-1}
>> for (i in 1:20){tot[i]<-(test[i]+tot[i])}
>> tot
>  [1] 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
> 
At the start numeric(20) gives you a vector of 20 zeros.  Your first 
loop changes all the values of test to 1.  Your second loop adds a one 
from test to each of the zeros in tot.

Simulating something like this by hand is a good way to spot the errors: 
  reduce the length of vector to some small number (e.g. 5), then write 
down on a piece of paper 5 slots for test, 5 for tot, and run through 
the commands as though you are R.  If you don't get what R gives at the 
end, then look at all the variables in your simulation, and identify 
where it went wrong.

Duncan Murdoch