2d lists

[SunX]

What is the best way to assign a 2d lists? Something like;

for i in range(10):
for j in range(10):
aList[i][j] = i*j

Thank you in advance.

[Jeff Epler]

Re: 2d lists

Depending on your purposes, you may be looking for numarray[1].[color=blue][color=green][color=darkred]
>>> import numarray
>>> anArray = numarray.fromfu nction(lambda x, y: x*y, (10,10))
>>> anArray[/color][/color][/color]
array([[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
[ 0, 2, 4, 6, 8, 10, 12, 14, 16, 18],
[ 0, 3, 6, 9, 12, 15, 18, 21, 24, 27],
[ 0, 4, 8, 12, 16, 20, 24, 28, 32, 36],
[ 0, 5, 10, 15, 20, 25, 30, 35, 40, 45],
[ 0, 6, 12, 18, 24, 30, 36, 42, 48, 54],
[ 0, 7, 14, 21, 28, 35, 42, 49, 56, 63],
[ 0, 8, 16, 24, 32, 40, 48, 56, 64, 72],
[ 0, 9, 18, 27, 36, 45, 54, 63, 72, 81]])

A cheap trick is to use tuples as dict keys, which gets you a kind of
sparse N-dimensional array:
aDict = {}
for i in range(10):
for j in range(10):
aDict[i,j] = i*j

You can create your nested list with a nested list comprehension:
aList = [ [ i * j for i in range(10) ] for j in range(10) ]
if you really want lists.

Jeff
[1] http://www.google.com/search?q=numarray

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[Shalabh Chaturvedi]

Re: 2d lists

SunX wrote:[color=blue]
> What is the best way to assign a 2d lists? Something like;
>
> for i in range(10):
> for j in range(10):
> aList[i][j] = i*j
>
> Thank you in advance.[/color]

If you want a list of lists, you could do:

for i in range(10):
L = aList[i] = []
for j in range(10):
L[j] = i*j

A completely different option is to use a dict for 2d data:

d = {}

for i in range(10):
for j in range(10):
d[(i,j)] = i*j

Notice the index is a tuple.

--
Shalabh

[Shalabh Chaturvedi]

Re: 2d lists

Shalabh Chaturvedi wrote:
[color=blue]
> SunX wrote:
>[color=green]
>> What is the best way to assign a 2d lists? Something like;
>>
>> for i in range(10):
>> for j in range(10):
>> aList[i][j] = i*j
>>
>> Thank you in advance.[/color]
>
>
> If you want a list of lists, you could do:
>
> for i in range(10):
> L = aList[i] = []
> for j in range(10):
> L[j] = i*j[/color]

This is quite wrong. Here is a corrected version (this time tested :)

aList = []
for i in range(10):
L = []
aList.append(L)
for j in range(10):
L.append(i*j)

--
Shalabh

[Piet van Oostrum]

Re: 2d lists

>>>>> xiaohua_sun@yah oo.com (SunX) (S) wrote:

S> What is the best way to assign a 2d lists? Something like;
S> for i in range(10):
S> for j in range(10):
S> aList[i][j] = i*j

S> Thank you in advance.

Use list comprehension:
aList = [[i*j for j in range(10)] for i in range(10)]
--
Piet van Oostrum <piet@cs.uu.n l>
URL: http://www.cs.uu.nl/~piet [PGP]
Private email: P.van.Oostrum@h ccnet.nl