[R] question regarding vector ops

[Uwe Ligges]

Rajarshi Guha wrote:

> Hi,
>   I was playing with some code and came upon this situation.
> 
> 
>>x <- c(1, rep(0,9))
>>x
> 
>  [1] 1 0 0 0 0 0 0 0 0 0
> 
>>idx <- 1:10
>>x[idx] <- x[idx] + 1
>>x
> 
>  [1] 2 1 1 1 1 1 1 1 1 1
> 
> This is expected. But if I do:
> 
> 
>>x <- c(1, rep(0,9))
>>x
> 
>  [1] 1 0 0 0 0 0 0 0 0 0
> 
>>idx <- rep(0,10)
>>idx
> 
>  [1] 0 0 0 0 0 0 0 0 0 0
> 
>>x[idx] <- x[idx] +1
>>x
> 
>  [1] 1 0 0 0 0 0 0 0 0 0
> 
> I was expoecting that when all the elements of idx are set to 0,
> x[0] would become 11.
> 
> Could somebody explain why this behavior occurs?


Why do you expect anything to become 11? And what is x[0] in your 
expectation?


x[0] is "empty" (indexing is starting from 1 in R) and returns 
numeric(0), hence
    x[0] <- anything
consequently does nothing ... (alternatively, one might expect an error 
message).


Uwe Ligges




> Thanks,
> 
> 
> -------------------------------------------------------------------
> Rajarshi Guha <rxg218 at psu.edu> <http://jijo.cjb.net>
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