R help - Oct 2011 - zoo arithmetics

Dear list members,

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


   > 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)

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)
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT

On Mon, 24 Oct 2011, 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?
It's a _feature_ that zoo first matches the index positions, uses only 
their intersection, and then performs arithmetic. This is also documented 
in Section 2.5 of vignette("zoo", package = "zoo").

The reason for this behaviour is, of course, that you would want to align 
computations between different series, in particular a series and its 
lags.

If you want to ignore the time index of one or more elements in 
mathematical operations, use coredata(z).

hth,
Z
>
>   > 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)
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>