Hello to the list !
A list of lists is the most logical construction.
But -- you don't need to assemble the rows separately --
this works too:
>>> my_matrix_as_lists = [ [4, 6, 8, 1],\
... [2, 5, 1, 3],\
... [2, 1, 2, 8] ]
>>> print my_matrix_as_lists[1][1]
5
Rob
On Dec 19, 2004, at 1:31 PM, Brian van den Broek wrote:
Bugra Cakir said unto the world upon 2004-12-19 10:33:
hi,
I want to create a matrix in Python. For example 3x4 how can i
create this? thanks
_______________________________________________
Tutor maillist - [EMAIL PROTECTED]
http://mail.python.org/mailman/listinfo/tutor
Hi,
at least two ways using only builtins occur to me:
1) A list of lists:
.>>> row1 = [4, 6, 8, 1]
.>>> row2 = [2, 5, 1, 3]
.>>> row3 = [2, 1, 2, 8]
.>>> my_matrix_as_lists = [row1, row2, row3]
.>>> print my_matrix_as_lists[1][1]
5
Note that
>>> row1[1]
6
since indicies start at 0.
2) To get around that, and be more efficient with matricies with many
empty cells:
.>>> my_matrix_as_dict = {(1,1):4, (1,2):6, (1,3):8,
(2,1):56, (2,3):12,
(3,1):3, (3,2):3}
.>>> my_matrix_as_dict[(3,1)]
3
.>>> my_matrix_as_dict[(2,1)]
56
So, you just can use the tuple co-ordinates you've defined in order to
access cells. Note also that the list way you'd have to represent
empty cells with a standard null value -- None is the usual choice.
But this way, you just don't define some tuples as keys, as I didn't
define (2,2) as a key. Thus:
.>>> my_matrix_as_dict[(2,2)]
Traceback (most recent call last):
File "<pyshell#19>", line 1, in -toplevel-
my_matrix_as_dict[(2,2)]
KeyError: (2, 2)
You can make that more graceful with a try/except block:
.>>> try:
my_matrix_as_dict[(2,2)]
except KeyError:
print "That cell is empty"
That cell is empty
.>>>
HTH,
Brian vdB
_______________________________________________
Tutor maillist - [EMAIL PROTECTED]
http://mail.python.org/mailman/listinfo/tutor
_______________________________________________
Tutor maillist - [EMAIL PROTECTED]
http://mail.python.org/mailman/listinfo/tutor
