[R] Is there any way to know when a field is blank

[Leeds, Mark (IED)]

I have many text files in the format below and in certain rare instances
such as below there can be nothing in one of the fields so
a double comma is written but I won't know this because I am reading in
many,many files sequentially.

# TEXT FILE

2004-02-10 00:01:31.00000,,105.60000000
2004-02-10 00:01:32.00001,,105.60000000
2004-02-10 00:01:45.00000,,105.60000000
2004-02-10 00:01:49.00000,,105.61000000
2004-02-10 00:02:08.00000,,105.60000000
2004-02-10 00:02:15.00000,,105.60000000
2004-02-10 00:02:23.00000,,105.60000000
2004-02-10 00:02:41.00000,,105.60000000
2004-02-10 00:03:09.00000,,105.59000000
2004-02-10 00:03:16.00000,,105.60000000
2004-02-10 00:03:19.00000,,105.59000000
2004-02-10 00:03:25.00000,,105.60000000
2004-02-10 00:03:39.00000,,105.59000000
2004-02-10 00:03:52.00000,,105.60000000
2004-02-10 00:03:54.00000,,105.60000000

# LINES OF CODE

fxdata<-read.zoo(file=fxfile,FUN=as.POSIXct,sep=",",col.names=c("date","
bid","ask"))
fxdata<-fxdata[( fxdata[,"bid"] > 0.0 ) & ( fxdata[,"ask"]  > 0.0 ),]
aggfxdata<-as.zoo(aggregatebyminutes(zooobj=fxdata,aggtimeframe=aggtimef
rame))

#=======================================================================
====================

Even with the double comma being there, the fxdata<-read.zoo line and
the fxdata<-fxdata line still work but then on
the aggfxdata<-as.zoo line , I get the error :

"Error in rep.int(seq(1:d[i]), prod(d[seq(length = i - 1)]) * rep.int(1,
: 
        invalid number of copies in rep()"

This error is reasonable because the routines, aggregatebyminutes,
probably has a problem with nothing
being in the bid field. My question is if there is some way tha I can
know that nothing
is in the bid field so that I can skip this file altogether and go onto
the next one ?
I'm not showing the details of the function because I'm not interested
in the error. I am only interested in knowing
that the "bid" field does not exist.

I ask only because I am unsure how often this double comma/missing field
scenario can happen so it would
be better to automate the skipping of the file.

Thanks.
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