as jim pointed out ( i think we were figuring this out simultaneously.
thanks a lot jim ), it looks it does have something to do with the 
fact that it's a zoo object because below i consider two cases.
 
in the first case, fxdatab is a zoo object and i get the length of temp
to be 1.
in the second case, fxdatac is a matrix and the results in temp are
correct.
 
gabor : i really hate to bother you because i already do WAY too much so
if
unclass as jim figured out and then as.zooing afterwards with the
original index is what you suggest, that's fine with me.
 
#-----------------------------------------------------------------------
------------------------------------------------------------------------
----------------------------------
 
fxdatab<-structure(c(0,4,0,4,0,4,0,4),.Dim=c(4,2),.Dimnames =
list(c("1","2","3","4"),c("bid","ask")),
index=structure(c(1144049400,1144049400,1144049400,1144050402),class=c("
POSIXt","POSIXct"),tzone = ""),class="zoo")
 
print(fxdatab)
 
fxdatab<-fxdatab[(( fxdatab[,"bid"] > 0.0 ) & ( fxdatab[,"ask"]  > 0.0
)),]
 
temp<-( fxdatab[,"bid"] > 0.0 ) & ( fxdatab[,"ask"]  > 0.0 )
 
print(temp)
print(length(temp))
print(sum(temp))
 
#-----------------------------------------------------------------------
---
 
fxdatac<-structure(c(0, 4, 0, 4, 0, 4, 0, 4), .Dim = c(4, 2), .Dimnames
= list(
    NULL, c("bid", "ask")))
 
print(fxdatac)
 
fxdatab<-fxdatac[(( fxdatab[,"bid"] > 0.0 ) & ( fxdatac[,"ask"]  > 0.0
)),]
 
temp<-( fxdatac[,"bid"] > 0.0 ) & ( fxdatac[,"ask"]  > 0.0 )
 
print(temp)
print(length(temp))
print(sum(temp))
--------------------------------------------------------

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