NA's in string vector.

[Vadim Kutsyy <vkutsyy@cytokinetics.com>]

Is there a way to define NA's in string vector?

> a<-c("a",NA,"b")
> is.na(a)
[1] F F F
> a
[1] "a"  "NA" "b" 
> a[2]<-NA
> is.na(a)
[1] F F F

Splus converge all NA's to "NA", which make problem in data.frames.

Thanks,
===================================================================
Vadim Kutsyy, PhD                             http://www.kutsyy.com
vkutsyy@cytokinetics.com                           vadim@kutsyy.com
Statistician                                      tel. 650-624-3218
Cytokinetics, Inc                                 fax. 650-624-3010
280 East Grand Avenue
South San Francisco, CA 94080           http://www.cytokinetics.com
===================================================================