445,909 Members | 2,008 Online
Need help? Post your question and get tips & solutions from a community of 445,909 IT Pros & Developers. It's quick & easy.

# 2D array

 P: n/a I'm wanting to do something with a list that is basically a 2 dimensional array. I'm not so good with lists so can someone give me an example of how I might implement this in Python? thanks. Jul 18 '05 #1
7 Replies

 P: n/a LutherRevisited wrote: I'm wanting to do something with a list that is basically a 2 dimensional array. I'm not so good with lists so can someone give me an example of how I might implement this in Python? thanks. If you're planning to do anything serious with a 2D array, you should probably look at numarray: http://www.stsci.edu/resources/softw...dware/numarray import numarray as na arr = na.array(range(10), shape=(5, 2)) arr array([[0, 1], [2, 3], [4, 5], [6, 7], [8, 9]]) arr[0,1] 1 arr[4,0] 8 If you're not doing any heavy computation, you can probably do this with nested lists: arr = [[0, 1], .... [2, 3], .... [4, 5], .... [6, 7], .... [8, 9]] arr[0][1] 1 arr[4][0] 8 Steve Jul 18 '05 #2

 P: n/a On Tue, 2004-12-07 at 23:02, Steven Bethard wrote: LutherRevisited wrote: I'm wanting to do something with a list that is basically a 2 dimensional array. I'm not so good with lists so can someone give me an example of how I might implement this in Python? thanks. If you're planning to do anything serious with a 2D array, you should probably look at numarray: http://www.stsci.edu/resources/softw...dware/numarray >>> import numarray as na >>> arr = na.array(range(10), shape=(5, 2)) >>> arr array([[0, 1], [2, 3], [4, 5], [6, 7], [8, 9]]) >>> arr[0,1] 1 >>> arr[4,0] 8 If you're not doing any heavy computation, you can probably do this with nested lists: >>> arr = [[0, 1], ... [2, 3], ... [4, 5], ... [6, 7], ... [8, 9]] >>> arr[0][1] 1 >>> arr[4][0] 8 Steve If your data is sparse you might want to consider using a dictionary where the key is a tuple representing the coordinates. a = {} a[(0,0)] = 0 a[(0,1)] = 1 a[(1,0)] = 2 a[(1,1)] = 3 a[(2,0)] = 4 a[(2,1)] = 5 a[(3,0)] = 6 a[(3,1)] = 7 a[(4,0)] = 8 a[(4,1)] = 9 a.get( (3,0), None ) 6 print a.get( (5,0), None ) None Adam DePrince Jul 18 '05 #3

 P: n/a Adam DePrince wrote: If your data is sparse you might want to consider using a dictionary where the key is a tuple representing the coordinates. a = {} a[(0,0)] = 0 a[(0,1)] = 1 [snip]print a.get( (5,0), None ) Good point. Note that you don't need the parentheses in the assignments or item accesses: a = {} a[0,0] = 10 a[0,0] 10 Also note that you don't need to specify None as the default value when you call dict.get -- None is assumed if no default value is supplied: print a.get((5, 2)) None Steve Jul 18 '05 #4

 P: n/a On Wed, 2004-12-08 at 15:06, Steven Bethard wrote: Adam DePrince wrote: If your data is sparse you might want to consider using a dictionary where the key is a tuple representing the coordinates. a = {} a[(0,0)] = 0 a[(0,1)] = 1 [snip]>print a.get( (5,0), None ) Good point. Note that you don't need the parentheses in the assignments or item accesses: >>> a = {} >>> a[0,0] = 10 >>> a[0,0] 10 Also note that you don't need to specify None as the default value when you call dict.get -- None is assumed if no default value is supplied: The use of None as the default parameter was on purpose; the lack of "magic" in python is often cited in religious wars between python and perl aficionados. Use of get(something, None) was on purpose, the level of familiarity with the language implied by the original question suggested that the notion of optional parameters, and specifically those of get, may not have been immediately obvious. As for a[0,0] instead of a[(0,0)] ... the former just *looks* so aesthetically wrong to me that I've never used it, and had forgotten that it was even possible. >>> print a.get((5, 2)) None Steve Adam DePrince Jul 18 '05 #5

 P: n/a Adam DePrince wrote: The use of None as the default parameter was on purpose; the lack of "magic" in python is often cited in religious wars between python and perl aficionados. Use of get(something, None) was on purpose, the level of familiarity with the language implied by the original question suggested that the notion of optional parameters, and specifically those of get, may not have been immediately obvious. As for a[0,0] instead of a[(0,0)] ... the former just *looks* so aesthetically wrong to me that I've never used it, and had forgotten that it was even possible. Sorry, I hadn't meant any of my comments as criticisms -- just wanted to make sure the OP knew about all the options open to them. I'm used to a[0,0] because I've used numarray a bit, but to each his own, of course. =) Steve Jul 18 '05 #6

 P: n/a I am also not here to criticize style here, but I want to point something out. Something like a[1,2] might look wrong, but it's actually parsed specially by Python to accommodate slicing of multidimensional arrays. The difference is that, inside [], you can use slicing syntax, as in a[1:2,3:4]. But using parentheses forces it to be parsed as an ordinary tuple, where you can't use slicing syntax. Thus, a[(1:2,3:4)] is a syntax error. Obviously this is irrelevant for dicts. But if you're using some sort of custom array object, that supports slicing in multiple dimensions, you can't slice with the parentheses. Because of this, I don't use the parentheses for things like multidimensional arrays. I tend to use the parentheses whenever the index is some sort of atomic value, however. -- CARL BANKS Jul 18 '05 #7

 P: n/a On Wed, 2004-12-08 at 16:22, Steven Bethard wrote: Adam DePrince wrote: The use of None as the default parameter was on purpose; the lack of "magic" in python is often cited in religious wars between python and perl aficionados. Use of get(something, None) was on purpose, the level of familiarity with the language implied by the original question suggested that the notion of optional parameters, and specifically those of get, may not have been immediately obvious. As for a[0,0] instead of a[(0,0)] ... the former just *looks* so aesthetically wrong to me that I've never used it, and had forgotten that it was even possible. Sorry, I hadn't meant any of my comments as criticisms -- just wanted to make sure the OP knew about all the options open to them. I'm used to a[0,0] because I've used numarray a bit, but to each his own, of course. =) Even if you were, there is certainly no need to apologize. In hindsight, my response seems rather naive; as naive perhaps as the students in my freshman year undergrad C class who having grown up on Turbo pascal would add to their programs: #define BEGIN { #define END { because it "looked right." Adam DePrince Jul 18 '05 #8

### This discussion thread is closed

Replies have been disabled for this discussion.