Coercing a character zoo to a numeric

Dear R-helpers,

It seems to me that a character zoo cannot be coerced to a numeric zoo.
Below is a minimal example. Can someone tell me what I have done wrong?

z<-zoo(1:4,order.by=1:4)
coredata(z)<-as.character(coredata(z))
str(z)

?zoo? series from 1 to 4
?Data: chr [1:4] "1" "2" "3" "4"
?Index: ?int [1:4] 1 2 3 4

coredata(z)<-as.numeric(coredata(z))
str(z)

?zoo? series from 1 to 4
?Data: chr [1:4] "1" "2" "3" "4"
?Index: ?int [1:4] 1 2 3 4

See ?zoo where it says that the zoo object may be "a numeric vector,
matrix or a factor".

Thus character is not supported although I suspect that a number of
operations continue to work anyways -- although evidently not that
one.

This seems to result in a numeric zoo object:

aggregate(z, identity, as.numeric)

although these sorts of computations with zoo objects that strictly
speaking are not legal are, of course, not officially supported.

Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com