Entry

Two-dimensional arrays

Jul 5th, 2000 10:00
Nathan Wallace, unknown unknown, Hans Nowak, Snippet 128, David Ascher

"""
Packages: basic_applications.arrays
"""
"""
> I have a problem that needs two-dimensional arrays, but NumPy really seems
> like overkill. I had solved it another way, then realized I really
> *needed* two-dimensional arrays.
Here's a little something based, as was suggested, on a list of arrays.
It's incomplete, but it should be a start -- while it only deals with
'single-attribute arrays', it shouldn't be too hard to make a
"multiattributemat' which builds on Mat to deal w/ multivalued arrays.
"""
"""
usage:
x = Mat((10,10), 'i')
x[0] = [4]*10
x[1][4:10] = x[0][:6]
x[2] = x[0]
etc.
"""
from array import array
import string
class Mat:
    defaults = {}
    for d in ('bBhHiIlLfd'): defaults[d] = 0.0
    defaults['c'] = ' '
    def __init__(self, (width, height), typecode, default=None):
	assert Mat.defaults.has_key(typecode)
	self.rows = [None]*height
	self.width = width
	self.height = height
	self.typecode = typecode
	for i in range(height):
	    if default is None:
		init = [Mat.defaults[typecode]]*width
	    else:
		if type(default) in (type(()), type([])):
		    assert len(default) == width
		    init = default
		else:
		    init = default*width
	    self.rows[i] = array(typecode, init)
    def __getslice__(self, start, end):
	return self.rows[start:end]
    def __getitem__(self, item):
	if type(item) == type(()):
	    assert len(item) == 2
	    i,j = item
	    return self.rows[i][j]
	elif type(item) == type(0):
	    return self.rows[item]  # shared reference!
	elif type(item) == type(slice(0,1,1)):
	    # deal with extended slices
	    raise "Unimplemented"
    def __setitem__(self, item, value):
	if type(item) == type(()):
	    assert len(item) == 2
	    i,j = item
	    self.rows[i][j] = value
	elif type(item) == type(0):
	    assert len(value) == self.width
	    value = list(value)
	    self.rows[item] = array(self.typecode, value)
	elif type(item) == type(slice(0,1,1)):
	    # deal with extended slices
	    raise "Unimplemented"
    def __repr__(self):
	rows = []
	for r in self.rows:
	    rows.append(str(r)[len("array('i', "):-1])
	return string.join(rows, ',\n')
x = Mat((10,10), 'i')
print x