Re: Why is importing the table into Mathematica so slow???
- To: mathgroup at smc.vnet.net
- Subject: [mg37877] Re: [mg37864] Why is importing the table into Mathematica so slow???
- From: "Johannes Ludsteck" <johannes.ludsteck at wiwi.uni-regensburg.de>
- Date: Sat, 16 Nov 2002 01:15:45 -0500 (EST)
- Organization: Universitaet Regensburg
- Sender: owner-wri-mathgroup at wolfram.com
Dear Jia,
the Import function of Mathematica is very slow. If
all entries in your Matrix have the same type, you can
use ReadList["file",Table[Number,{750}]]. This is may
be hundred times faster.
If your entries have different types, use
ReadList["file",Table[Word,{750}]].
Then all entries are read as strings. You can convert
the Strings containing numbers then with ToExpression.
Applying ToExpression for the non-numeric rows or
colums will also be much faster (probably by a factor
of 100).
Best regards
Johannes
On 15 Nov 2002 at 1:36, Jia Guo wrote:
> Hi,
>
> I currently have such a problem in Mathematica:
>
> I have a matrix of size 750*750. It is in a file and I will import the
> file to Mathematica using the command: g = Import ["matrix.dat",
> "Table"].
>
> However, it took me over 2 hours to import and display the numbers in
> the notebook. But the transpose and reverse operations to the matrix
> are really fast: 4-5 seconds. I translated the matrix into a graph and
> when I was going to export it, the same problem happened. It slowed
> down again.
>
> Does anybody know what should I do to avoid the big overhead?
>
> Thank you!
>
> Jia
>
<><><><><><><><><><><><>
Johannes Ludsteck
Economics Department
University of Regensburg
Universitaetsstrasse 31
93053 Regensburg
Phone +49/0941/943-2741