[R] ifelse help?

[rkevinburton at charter.net]

Sorry I didn't give the proper initialization of j. But you are right j should also be an array of 5. So x[j + 5] would return 5 values. 

So if the array returned from 'ifelse' is the same dimention as test (h), then are all the values of h being tested? So since h as you say has no dimensions is the test only testing h[1]? Again it seems that if all of the elements of h are tested (there are 5 elements) and each element produces an array of 5 the resulting array should be 25. 

Kevin

---- "Charles C. Berry" <cberry at tajo.ucsd.edu> wrote: 
> On Mon, 19 Jan 2009, rkevinburton at charter.net wrote:
> 
> > I am having a hard time understanding what is happening with ifelse.
> >
> > Let me illustrate:
> >
> > h <- numeric(5)
> > p <- 1:5
> > j <- floor(j)
> 
> And j is 0:4 + epsilon , where 0 <= epsilon < 1, evidently.
> 
> > x <- 1:1000
> > ifelse(h == 0, x[j+2], 1:5)
> > [1] 2 3 4 5 6
> >
> > My question is, "shouldn't this be retruning 25 numbers?"
> 
> 
> No. It should be
> 
>  	A vector of the same length and attributes (including class) as
>  	test and data values from the values of yes or no
> 
> according to ?ifelse, and 'test' is what you have as 'h'
> 
> Consider
> 
> > z <- as.data.frame( diag(2 ) )
> >  ifelse(z == 0, letters , 1:5)
>       V1  V2
> [1,] "1" "c"
> [2,] "b" "4"
> >
> 
> all args have different lengths and classes. But the result has those of 
> the 'test' arg.
> 
> 
> > It seems that the ifelse should check 5 values of h for zero. For each 
> > of the 5 values I am thinking it should return an array of 5 (x[j+2] if 
> > h[index] == 0). Since the dimension of h is 5 that would mean 25 values.
> 
> h has no attributes, therefore no 'dimension'
> 
> HTH,
> 
> Chuck
> 
> > But that isn't what is being returned.Something about this that I don't 
> > understand. Please help my ignorance.
> >
> > Thank you.
> >
> > Kevin
> >
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> >
> 
> Charles C. Berry                            (858) 534-2098
>                                              Dept of Family/Preventive Medicine
> E mailto:cberry at tajo.ucsd.edu	            UC San Diego
> http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901
> 
>