Trouble with subset.ff

Dear all

I am having trouble with subsetting an ffdf object, hopefully somebody can help...

I have an index, which is a ff object of vmode "logical":

index.SAS

ff (open) logical length=4977231 (4977231)
       [1]       [2]       [3]       [4]       [5]       [6]       [7]       [8]           [4977224] [4977225] [4977226] [4977227] [4977228] [4977229]
      TRUE      TRUE      TRUE      TRUE      TRUE      TRUE      TRUE      TRUE         :      TRUE      TRUE      TRUE      TRUE      TRUE      TRUE
[4977230] [4977231]
      TRUE      TRUE

I would like to use this index to subset the ffdf object "data.SAS". 
The number of rows in data.SAS equals the length of index.SAS. 
However, the command

Missing.data <- subset(data.SAS, !index.SAS)

gives me the following error:

Error in ffdf(x = x) : ffdf components must be atomic ff objects

A similar command also results in an error:

Missing.data <- data.SAS[!index.SAS,]

Error: vmode(index) == "integer" is not TRUE

I do not want to use "index.SAS[]" (which works in many cases, but sometimes crashes), because - as far as I understand - this will cause trouble with really large index vectors (I would prefer using ff objects).

So I came up with the following syntax, which seems to work:

Missing.data <- data.SAS[ffwhich(index.SAS,index.SAS==FALSE),]

...I am just not sure if this is the right approach.

I am running


platform       i386-w64-mingw32

arch           i386

os             mingw32

system         i386, mingw32

status

major          3

minor          0.3

year           2014

month          03

day            06

svn rev        65126

language       R

version.string R version 3.0.3 (2014-03-06)

nickname       Warm Puppy


with ffbase_0.11.3 and ff_2.2-12


Many thanks in advance
Christian

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