[R] zoo arithmetics

[David Winsemius]

On Oct 23, 2011, at 9:35 PM, Hugo Mildenberger wrote:

> Dear list members,
>
> what is the reason that one obviously can't do arithmetic operations  
> on
> zoo members with different index positions?

zoo-objects are designed to merged by their indices before applying  
arithmetic operations.

You are essentially adding across rows of:

 > merge(z[1],z[2])
   z[1] z[2]
1    1   NA
2   NA    1

  You have no overlapping indices so you get nothing.

 > z2 <- zoo(10:15,order.by=1:6)
 > z2+z
  1  2  3
11 12 13    # Only get results where the indices "line up".

>
>> require(zoo)
>> z <- zoo(c(1,1,1),order.by=c(1,2,3))
>> z
>   1 2 3
>   1 1 1
>> z[1]   + z[1]
>   1
>   2
>> z[1:2] + z[1:2]
>   1 2
>   2 2
>> z[1] + z[2]
>   Data:
>   numeric(0)
>
>   Index:
>   numeric(0)
>
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David Winsemius, MD
West Hartford, CT