[Rd] Use logical expresion on ff object

[Krystian Radlak]

It's not corect. Vector with length 15*10^6 you could store in memory without
ff packages.
For vector 15*10^7

 k=bit(15*10^7) 
 a=ff(2,15*10^7) 
 system.time(k<-a[,chunk(1,length.ff(a),1e4)]<1)

Error: cannot allocate vector of size 572.2 Mb
In addition: Warning messages:
1: In system.time(k <- a[, chunk(1, length.ff(a), 10000)] < 1) :
  Reached total allocation of 1535Mb: see help(memory.size)
2: In system.time(k <- a[, chunk(1, length.ff(a), 10000)] < 1) :
  Reached total allocation of 1535Mb: see help(memory.size)
3: In system.time(k <- a[, chunk(1, length.ff(a), 10000)] < 1) :
  Reached total allocation of 1535Mb: see help(memory.size)
4: In system.time(k <- a[, chunk(1, length.ff(a), 10000)] < 1) :
  Reached total allocation of 1535Mb: see help(memory.size)
Timing stopped at: 2.13 0.84 10.45 

And you don't understand my question. In simple operation in R I could do:
a=c(1,4,5,6)
b=a[a>1]
b
[1] 4 5 6

If a is ff object (for example length=15*10^7) this operation doesn't work.
Mayby I don't understand something or this operation is not definied
currently in this package. 
In summarizing:
I have very long vector stored in ff object and I want to chse elements from
this vector which fulfil logical expresion (for example a>1). 

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