[R-sig-DB] How to store R objects in blob in MySQL?

[Dirk Eddelbuettel]

On 8 February 2008 at 14:31, Rainer M Krug wrote:
| Hi
| 
| I was thinking - how can I store R objects in a blob field? Normal
| dataframes can be nicely stored in a table - but is theree a mechanism to
| store objects in a blob field?

I tried to answer that question in an email I sent you two days ago:

   From: Dirk Eddelbuettel <edd using eddelbuettel.com>
   To: Rainer M Krug <r.m.krug using gmail.com>
   Cc: Richard Pearson <richard.pearson using postgrad.manchester.ac.uk>,
   	R-help using r-project.org
   Subject: Re: [R] advice requested re: building "good" system (R, SQL db)
   	for handling large datasets
   Date: Wed, 6 Feb 2008 09:58:56 -0600
   
   On Wed, Feb 06, 2008 at 02:34:52PM +0200, Rainer M Krug wrote:
   > R objects in blobs - I never thought about that. Could you elaborate on how
   > to do something like that (I am using RMySQL)?
   
   Look at help(serialize) -- any R object can be turned into a suitable
   representation, either binary (more efficient) or ascii (possibly
   'safer'). 
   
   Store that, retrieve it later, reconstruct the object and be merry :) 
   
   > tmpDf <- data.frame(a=1:10, b=LETTERS[1:10], c=rnorm(10))
   > serDf <- serialize(tmpDf, NULL, ascii=TRUE)
   > rm(tmpDf)
   > head(unserialize(serDf))
     a b          c
     1 1 A -0.6945820
     2 2 B -0.2960084
     3 3 C -0.2514302
     4 4 D -0.7318635
     5 5 E -0.1698489
     6 6 F  0.4331521
     > 
   
   Dirk

Now, look at what serDf actually is -- an ascii vector.  You can simply write
that to virtually any db system into a char field of variable length.  You
could also create an actual blob object via
	serDfBin <- serialize(tmpDf, NULL, ascii=FALSE)
but you can't print that easily to the console for checks pp.  It is however
a binary blob, so if you wanted to write that, you could.

Does this help?

Dirk
	

| I am using MySQL under Linux.
| 
| Thanks
| 
| Rainer
| 
| 
| -- 
| Rainer M. Krug, Dipl. Phys. (Germany), MSc Conservation Biology (UCT)
| 
| Plant Conservation Unit Department of Botany
| University of Cape Town
| Rondebosch 7701
| South Africa
| 
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