[Rd] textConnection performance quadratic (PR#14053)

[bill.hopkins at level3.com]

Full_Name: William E. Hopkins
Version: 2.9.0
OS: Windows XP
Submission from: (NULL) (209.244.4.106)


textConnection() has quadratic performance.

A function I wrote was taking outrageous amount of time to execute on a large
character vector (small test set was used for functional development). I created
a test harness to execute the function and gather stats (system.time) for
various dataset sizes (datasets generated by sample() of very large set). If I
used textConnection() to provide input to read.csv(), the performance was
quadratic with dataset size. However, if I had the function write the character
vector to a temp file then read the data back in via read.csv, the performance
was linear.

The reason for using a textConnection() was that the character vector was within
a data frame read in via read.csv. The character vector (URLs) needed to be
parsed into separate vectors, but no mechanism exists to do that directly (that
I know of). So, I used sub() to extract the proper pieces and put commas in
between so that I can use read.csv() to read the comma-separate strings directly
into vectors.