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MathGroup Archive 1998

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Speeding up ReadList[]?




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





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