[R] zoo object: replace NAs from another zoo object

[Timothy W. Hilton]

Hello,

I have two zoo objects, new and old, indexed by chron objects.  Their structure is like this:

(05/25/06 00:00:00)     NA     NA  NA
(05/25/06 00:02:00) 948.20 24.198   0
(05/25/06 00:04:00) 948.26 20.640   0
(05/25/06 00:06:00) 948.37 19.653   0
(05/25/06 00:08:00) 948.48 19.135   0
(05/25/06 00:10:00) 948.54 22.510   0
(05/25/06 00:12:00) 948.55 27.175   0
(05/25/06 00:14:00) 948.46 30.075   0
(05/25/06 00:16:00) 948.59 28.815   0
(05/25/06 00:18:00) 948.96 27.938   0

old spans a larger range of dates than new.  I would like to take all the values in new that are not NA and place them in old, matching the time indices.  I have tried a number of variations on the themes of merge and replace, but can't get them to work, and the brute force for loop solution is unnacceptably slow.  Could someone suggest a solution?

Many thanks,
Tim