Python

Empty 2D Array

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Join Date: Dec 2008

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Reputation: Nanz is an unknown quantity at this point

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Nanz

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Empty 2D Array

Dec 3rd, 2008

Hello all.

I want to craete a empty double dimensional array.
Later i will get the row and column length. But row length varies each time program. But i will be having the lenght of the row. So hoe to write a generic code for creating a empty 2D array and dynamically insert values in it.

ASAP

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jlm699

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Re: Empty 2D Array

Dec 3rd, 2008

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Originally Posted by Nanz

hoe to write a generic code for creating a empty 2D array and dynamically insert values in it.

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
>>> arr_2d = [[]]
>>> arr_2d[0].append(0)
>>> arr_2d[0].append(1)
>>> arr_2d.append([3,4,5])
>>> arr_2d
[[0, 1], [3, 4, 5]]
>>>
>>> arr_2d = [[]]
>>> arr_2d[0].append(0)
>>> arr_2d[0].append(1)
>>> arr_2d.append([3,4,5])
>>> arr_2d
[[0, 1], [3, 4, 5]]
>>>

It might benefit you to create a 2d array class to handle the many different aspects of working with a 2d array.

1. Use Code Tags.
2. Homework? Show Effort.
3. Keep discussions on the forum: no PMs

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vegaseat

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Re: Empty 2D Array

Dec 3rd, 2008

Not sure if I follow this correctly, but you start with a one dimensional list and append other lists to it. For example ...

 Help with Code Tags 
 python Syntax (Toggle Plain Text) 
qq = []
for row in range(3):
    for col in range(3):
        qq.append([row, col])
 
print qq
 
"""
my output -->
[[0, 0], [0, 1], [0, 2], [1, 0], [1, 1], [1, 2], [2, 0], [2, 1], [2, 2]]
"""
qq = []
for row in range(3):
    for col in range(3):
        qq.append([row, col])
        
print qq

"""
my output -->
[[0, 0], [0, 1], [0, 2], [1, 0], [1, 1], [1, 2], [2, 0], [2, 1], [2, 2]]
"""

You could use None as a placeholder.

Last edited by vegaseat; Dec 3rd, 2008 at 11:25 am.

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solsteel

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Re: Empty 2D Array

Dec 3rd, 2008

I like using list comprehensions for this kind of task.

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
>>> cols = 4
>>> rows = 5
>>> array = [[0 for i in range(cols)] for j in range(rows)]
>>> array
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>>
>>> cols = 4
>>> rows = 5
>>> array = [[0 for i in range(cols)] for j in range(rows)]
>>> array
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
>>>

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woooee

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Re: Empty 2D Array

Dec 3rd, 2008

If it is easier to get your head around, you can use a dictionary of lists, with the dictionary key as the row number, each containing x columns. You could also take this one step further and use a dictionary of dictionaries with row and column number as keys.

 Help with Code Tags 
 Python Syntax (Toggle Plain Text) 
def populate_array(rows, columns):
   array_dic = {}
   for row in range(1, rows+1):     ## starts with one, not zero
      array_dic[row] = []
      for col in range(0, columns):
         array_dic[row].append('None')     ## initialize to 'None'
   return array_dic
 
if __name__ == "__main__":
   rows = 10
   columns = 5
   ret_dic = populate_array(rows, columns)
   for key in ret_dic.keys():
      print key, ret_dic[key]
 
   ##---  change some value
   row = 3
   col = 1
   ret_dic[row][col] = 'Changed'
   print "\n"
   for key in ret_dic.keys():
      print key, ret_dic[key]
def populate_array(rows, columns):
   array_dic = {}
   for row in range(1, rows+1):     ## starts with one, not zero
      array_dic[row] = []
      for col in range(0, columns):
         array_dic[row].append('None')     ## initialize to 'None'
   return array_dic
   
if __name__ == "__main__":
   rows = 10
   columns = 5
   ret_dic = populate_array(rows, columns)
   for key in ret_dic.keys():
      print key, ret_dic[key]
      
   ##---  change some value
   row = 3
   col = 1
   ret_dic[row][col] = 'Changed'
   print "\n"
   for key in ret_dic.keys():
      print key, ret_dic[key]