[Numpy-discussion] Numeric - fromfile ?

[Arnd Baecker]

On Tue, 23 Aug 2005, Alexandre Fayolle wrote:

> On Mon, Aug 22, 2005 at 01:27:55PM -0400, Hari Sundar wrote:
> > Hi,
> >
> > Is there a function similar to numarray's fromfile, to read a binary array
> > from a file ? What is the best way to read such a file into a Numeric array.

Another option is to use scipy.io, e.g.:

In [5]:scipy.io.fread?
Type:           builtin_function_or_method
Base Class:     <type 'builtin_function_or_method'>
String Form:    <built-in function fread>
Namespace:      Interactive
Docstring:
    g = numpyio.fread( fid, Num, read_type { mem_type, byteswap})

         fid =       open file pointer object (i.e. from fid =
open('filename') )
         Num =       number of elements to read of type read_type
         read_type = a character in 'cb1silfdFD' (PyArray types)
                     describing how to interpret bytes on disk.
    OPTIONAL
         mem_type =  a character (PyArray type) describing what kind of
                     PyArray to return in g.   Default = read_type
         byteswap =  0 for no byteswapping or a 1 to byteswap (to handle
                     different endianness).    Default = 0.


I use this a lot and it works very well.
For example:

    from scipy import *

    # --- Create some arrays:
    x=arange(10)/10.0

    z=zeros( (5,5),"d")
    z_complex=zeros( (5,7),"D")

    # --- write them as binary data:
    fp=file("x.dat","wb")
    io.fwrite(fp,len(x),x)
    fp.close()

    fp=file("z.dat","wb")
    io.fwrite(fp,z.shape[0]*z.shape[1],z)
    fp.close()

    fp=file("z_complex.dat","wb")
    io.fwrite(fp,z_complex.shape[0]*z_complex.shape[1],z_complex)
    fp.close()

    # --- and read them back
    fp=file("x.dat","rb")
    x_read=io.fread(fp,10,"d")
    fp.close()

    fp=file("z.dat","rb")
    z_read=reshape(io.fread(fp,5*5,"d"),(5,5))
    fp.close()

    fp=file("z_complex.dat","rb")
    z_complex_read=reshape(io.fread(fp,5*7,"D"),(5,7))
    fp.close()

Remark: `"wb"` and `"rb"` is only needed under Windows,
normally `"w"` and `"r"` would be enough.

Best,

Arnd