[SciPy-user] Creating a sparse matrix

[Robert Cimrman]

Nils Wagner wrote:
> On Thu, 13 Dec 2007 14:03:14 +0100
>   Robert Cimrman <cimrman3 at ntc.zcu.cz> wrote:
>> Nils Wagner wrote:
>>> Hi all,
>>>
>>> How can I build a sparse matrix from the following array 
>>> ?
>>>>>> data
>>> array([['1', '1', '1.7244067583090530E+05'],
>>>         ['1', '2', '4.7526228631699840E+04'],
>>> ...
>>>         ['18', '24', '-1.0245630931609220E+03'],
>>>         ['24', '24', '4.2234547103090340E+03']],
>>>        dtype='|S23')
>>>
>>> data contains information about row, column and the 
>>> corresponding entry.
>>>
>>> Any pointer would be appreciated.
>> You read the data from a file, right? 
> 
> Exactly.
> 
> You should convert
>> the row/column 
>> indices to integers and values to floats during the 
>> reading. 
> 
> How can I do that on-the-fly ?

Well, supposing the file is not too large:
     fd = open( ... )
     rows, cols, vals = [], [], []
     while 1:
         try:
             line = fd.readline()
             if (len( line ) == 0): break
             if len( line ) == 1: continue
         except EOFError:
             break
         line = line.split()
         ir, ic, val = int( line[0] ), int( line[1] ), float( line[2] )
         rows.append( ir )
         cols.append( ic )
         vals.append( val )

Alternatively, you can try to use numpy.fromfile( ..., sep = ' ', dtype 
= numpy.float64 ) and then reshape it to (n, 3) and re-type the first 
two columns to ints.

r.