[R] zoo arithmetics

[Achim Zeileis]

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)
>
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