Need help initializing a list or tuple.

[KraftDiner]

I need a matrix of 256 x 256 unsigned short values...
The matrix can be implemented as a list of lists or a tuple...
So for example:
[[1][2][3], [4][5][6], [7][8][9]]
or
((1,2,3),(4,5,6 ), (7,8,9))

This is what I have so far but its not working...

a = [][]
for i in range(0,256):
for j in range(0,256):
a[i][j] = i**2

[Fredrik Lundh]

Re: Need help initializing a list or tuple.

"KraftDiner " wrote:
[color=blue]
> I need a matrix of 256 x 256 unsigned short values...
> The matrix can be implemented as a list of lists or a tuple...
> So for example:
> [[1][2][3], [4][5][6], [7][8][9]]
> or
> ((1,2,3),(4,5,6 ), (7,8,9))
>
> This is what I have so far but its not working...
>
> a = [][]
> for i in range(0,256):
> for j in range(0,256):
> a[i][j] = i**2[/color]

this might help:

http://www.python.org/doc/faq/programming/#how-do-i-create-a-multidimensional-list

</F>

[KraftDiner]

Re: Need help initializing a list or tuple.

Thank you that worked great!

a = [[None] * 256] * 256
for i in range(0,256):
for j in range(0,256):
a[i][j] = i**2

Now.. Can I change this quickly into a 1 dimensional list of length
65536?

[Diez B. Roggisch]

Re: Need help initializing a list or tuple.

KraftDiner schrieb:[color=blue]
> Thank you that worked great!
>
> a = [[None] * 256] * 256
> for i in range(0,256):
> for j in range(0,256):
> a[i][j] = i**2
>
> Now.. Can I change this quickly into a 1 dimensional list of length
> 65536?[/color]

sum(a, [])

Diez

[KraftDiner]

Re: Need help initializing a list or tuple.

Strange behaviour...

a = [[None] * 256] * 256
for i in range(0,256):
for j in range(0,256):
a[i][j] = i**2
a = sum(a, [])
print a[0]
print a[65535]

Prints:

65025
65025

[Fredrik Lundh]

Re: Need help initializing a list or tuple.

"KraftDiner " wrote:
[color=blue]
> Strange behaviour...
>
> a = [[None] * 256] * 256
> for i in range(0,256):
> for j in range(0,256):
> a[i][j] = i**2
> a = sum(a, [])
> print a[0]
> print a[65535]
>
> Prints:
>
> 65025
> 65025[/color]

looks like you missed that the page I pointed you to explained *why*
the a = [[None] * 256] * 256 approach doesn't work...

</F>

[KraftDiner]

Re: Need help initializing a list or tuple.

Yes I missed the fine print that said that the code had 'side effects'
So:

a = [None]*256
for i in range(256):
a[i] = [None] * 256
for i in range(0,256):
for j in range(0,256):
a[i][j] = i**2

a = sum(a, [])
print a[0]
print a[65535]

[John Salerno]

Re: Need help initializing a list or tuple.

KraftDiner wrote:
[color=blue]
> [[1][2][3], [4][5][6], [7][8][9]][/color]

I'm confused. Is that a valid list?

[KraftDiner]

Re: Need help initializing a list or tuple.

Oh by the way the b = sum(a, []) worked well to convert the two
dimensional array to a 1D array...
Is there a way to bring that 1D array back to a 2D array?

[KraftDiner]

Re: Need help initializing a list or tuple.

nope.. sorry its not...
I meant x = [[1,2,3],[3,4,5],[5,6,7]]

[Blackbird]

Re: Need help initializing a list or tuple.

John Salerno wrote:[color=blue]
> KraftDiner wrote:
>[color=green]
>> [[1][2][3], [4][5][6], [7][8][9]][/color]
>
> I'm confused. Is that a valid list?[/color]

No. I'm assuming he meant [[1, 2, 3], [4, 5, 6], [7, 8, 9]].

[John Salerno]

Re: Need help initializing a list or tuple.

KraftDiner wrote:[color=blue]
> nope.. sorry its not...
> I meant x = [[1,2,3],[3,4,5],[5,6,7]]
>[/color]

Whew, you were about to really throw me for a loop otherwise! :)

[BranoZ]

Re: Need help initializing a list or tuple.

How about:

a = [ [i**2 for j in range(256)] for i in range(256) ]
b = sum(a, [])
c = [ b[slice(i,i+256)] for i in range(0,256*256 ,256) ][color=blue][color=green][color=darkred]
>>> a is c[/color][/color][/color]
False[color=blue][color=green][color=darkred]
>>> a == c[/color][/color][/color]
True

BranoZ

[cdunn2001@gmail.com]

Re: Need help initializing a list or tuple.

# Nested list comprehensions act like real for loops:[color=blue][color=green][color=darkred]
>>> a = [[None for i in range(3)] for j in range(3)]
>>> a[/color][/color][/color]
[[None, None, None], [None, None, None], [None, None, None]][color=blue][color=green][color=darkred]
>>> a[0][0] = 5
>>> a[/color][/color][/color]
[[5, None, None], [None, None, None], [None, None, None]]
# Side-effect: i and j will be changed.

# Another way (much less clear to my eyes):[color=blue][color=green][color=darkred]
>>> a = map(lambda x: map(lambda x: None, range(3)), range(3))
>>> a[0][0]=5
>>> a[/color][/color][/color]
[[5, None, None], [None, None, None], [None, None, None]]

[Terry Reedy]

Re: Need help initializing a list or tuple.


"KraftDiner " <bobrien18@yaho o.com> wrote in message
news:1141666188 .237150.320690@ j52g2000cwj.goo glegroups.com.. .[color=blue]
> Thank you that worked great!
>
> a = [[None] * 256] * 256
> for i in range(0,256):
> for j in range(0,256):
> a[i][j] = i**2
>
> Now.. Can I change this quickly into a 1 dimensional list of length
> 65536?[/color]

If 'a' were a Numeric/Numarray/NumPy array, then I believe you could
re-dimensionalize it on the fly to be 1x65536 instead of 256x256. See
numeric.scipy.o rg for more.

tjr