How to write efficiently a large matrix of real numbers to an ASCII file
- To: mathgroup at smc.vnet.net
- Subject: [mg7266] How to write efficiently a large matrix of real numbers to an ASCII file
- From: Martin Heimann <martin.heimann at dkrz.de>
- Date: Tue, 20 May 1997 02:59:18 -0400 (EDT)
- Organization: mpi für meteorologie
- Sender: owner-wri-mathgroup at wolfram.com
Dear fellow Mathematica users,
This seems to be a very basic question and must have been asked many
times before, maybe it is in a FAQ, but I could not find it.
How to write efficiently a matrix of real numbers to an ASCII file such
that it can be read by a normal program (e.g. in Fortran or C)?
WRI suggests to use WriteMatrix:
WriteMatrix[filename_String,data_List,separator_String:"\t"] :=
With[{myfile = OpenWrite[filename]},
Scan[(WriteString[myfile,First[#]];
Scan[WriteString[myfile,separator,#]&,Rest[#]];
WriteString[myfile,"\n"])&,data];
Close[myfile]]
which, however, does not write exponents in the standard "e" format.
Furthermore, WriteMatrix is very slow (try it on a matrix of 1000 x 10
real numbers!).
The exponents are written correctly if one uses FortranForm to write the
individual numbers:
WriteFMatrix[filename_String,data_List,separator_String:"\t"] :=
With[{myfile = OpenWrite[filename]},
Scan[(WriteString[myfile,FortranForm[First[#]]];
Scan[WriteString[myfile,separator,
FortranForm[#]]&,Rest[#]];
WriteString[myfile,"\n"])&,data];
Close[myfile]]
This is still very slow, however. Has anybody a faster suggestion? Maybe
by using Compile[]?
I'd appreciate very much your suggestions.
Martin Heimann (martin.heimann at dkrz.de)