[R] Raw data type transformations

From: <dhinds_at_sonic.net>
Date: Thu 18 Aug 2005 - 04:39:08 EST


Not sure if this belongs here or on the devel list:

I've needed a more efficient way to manipulate raw binary data in R, with more than the minimal raw transformation functions in the base package. So I've written a small package in C that effectively lets me cast back and forth between raw vectors and other data types.

I've implemented four functions: rawToHex, hexToRaw, readRaw, and writeRaw. The first two convert between raw vectors and hex character strings. I use these to work around a limitation of ROracle not directly supporting raw data types, but they may have other uses. readRaw and writeRaw are similar to readBin and writeBin, but operate on raw vectors in place of binary connections, and I took a few shortcuts in my implementation (I handle a subset of data types and didn't implement byte swapping).

[aside: Rinternals.h does not export RAW() for packages]

I first thought there might be a way to do this via connections but didn't want to actually read and write files just to map between data types. One option would be to implement a rawConnection() analog of the current textConnection(), which would associate raw vectors with binary connections, and allow readBin()/writeBin().

Looking at the text connection code, it seems to me that it could be extended to handle this fairly easily. For input connections, it appears that all that needs to be done is to add support for filling the internal buffer from a raw vector (a few lines of code), and adding a text_read() function (again just a few lines). For output, text_write() is similarly simple, and a few lines of code would need to be added to text_vfprintf() to handle copying to a raw vector in place of a character vector.

The text_* functions would then probably be better named internal_* since they would handle internal binary as well as internal text connections.

Does this sound like it would be a useful capability?


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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Thu Aug 18 05:05:49 2005

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