[R] Compression data to variable using gzcon

[Jan van der Laan]

I wanted to compress a raw vector into another raw vector. This problem 
is solved using memCompress. However before discovering this function, I 
first tried to get this working using gzcon. From the documentation it 
seems that this should be possible:

 >     Compressed output will contain embedded NUL bytes, and so ‘con’ is
 >     not permitted to be a ‘textConnection’ opened with ‘open = "w"’.
 >     Use a writable ‘rawConnection’ to compress data into a variable.

But I can't seem to get this to work:

 > data <- as.raw(sample(0:255, 100))
 > con <- rawConnection(raw(0), "wb")
 > zz  <- gzcon(con)
 > writeBin(data, zz)
 > val <- rawConnectionValue(con)
Error in rawConnectionValue(con) :
   internal connection is not a rawConnection

The documentation of gzcon does mention that the original connection 
becomes unusable. Ok, so this error is to be expected. But how do I get 
to the compressed data?

As I mentioned memCompress(data) does what I want, so the the problem of 
compressing the data itself is solved, but I would like to understand 
how to use gzcon.

Thanks.

Jan