[Date Index] [Thread Index] [Author Index]

Speeding up ReadList[]?

• To: mathgroup@smc.vnet.net
• Subject: [mg12020] Speeding up ReadList[]?
• From: sidles@u.washington.edu (John Sidles)
• Date: Fri, 17 Apr 1998 03:40:55 -0400
• Organization: University of Washington, Seattle

I use Mathematica to process Excel spreadsheets containing large arrays
({500,500}) of ASCII-coded floats.  To read in the lists, I use the
Mathematica function

      ReadList[stream, Number, RecordLists->True]

Everything works fine, except that as each new array, is read and
processed, ReadList[] gets slower and s l o w e r and
s...l...o...w...e...r.  The first ReadList[] takes only 40 seconds,
while the second ReadList[] can take 400 seconds or longer, and I don't
even know how long the third ReadList[] takes.

Each file is processed independently, and no large arrays are retained
in memory (they are stored as local variables inside Module[] blocks). 
VIrtual memory is not used, and both the Kernel and the Notebook retain
plenty of unallocated memory.

Each file does generate a large Graphics[] object, but surprisingly,
Mathematica does not slow down while computing each graphic.  Thus,
ReadList[] is the only function evidencing a slowdown.

Neither the MathSource nor the FAQ seem to address this problem.  Has
anyone else run into this slowdown, and  how can it be avoided?

Thanks ... JAS

• Follow-Ups:
  • Re: Speeding up ReadList[]?
    • From: Sean Ross <seanross@worldnet.att.net>