2D arrays in Python

Question

What s the best way to create 2D arrays in Python   What I want is want is to store values like this   X   Y   Z   so that I access data like X 2  Y 2  Z 2  or X n  Y n  Z n  where n is variable  I don t know in the beginning how big n would be so I would like to append values at the end

User · Answer

In Python one would usually use lists for this purpose  Lists can be nested arbitrarily  thus allowing the creation of a 2D array  Not every sublist needs to be the same size  so that solves your other problem  Have a look at the examples I linked to

User · Answer

I would suggest that you use a dictionary like so   arr       arr 1     1  2  4  arr 18     3  4  5   print arr 1    gt  gt  gt   1  2  4    If you re not sure an entry is defined in the dictionary  you ll need a validation mechanism when calling  arr x    e g  try-except

User · Answer

If you are concerned about memory footprint  the Python standard library contains the array module  these arrays contain elements of the same type

User · Answer

x list   def enter n       y list       for i in  range 0 n           y append int input  Enter          return y for i in range 0 2       x insert i enter 2   print  x    here i made function to create 1-D array and inserted into another array as a array member  multiple 1-d array inside a an array  as the value of n and i changes u create multi dimensional arrays

User · Answer

Depending what you re doing  you may not really have a 2-D array   80  of the time you have simple list of  row-like objects   which might be proper sequences   myArray       pi  3 14159  r  2     e  2 71828  theta   5     myArray 0  1     3 14159 myArray 1  1     2 71828   More often  they re instances of a class or a dictionary or a set or something more interesting that you didn t have in your previous languages   myArray       pi  3 1415925  r  2     e  2 71828  theta   5      20  of the time you have a dictionary  keyed by a pair  myArray      2009  aug    some tuple of values    2009  sep    some other tuple      Rarely  will you actually need a matrix   You have a large  large number of collection classes in Python  Odds are good that you have something more interesting than a matrix

User · Answer

Please consider the follwing codes   from numpy import zeros scores   zeros  len chain1  len chain2    float

User · Answer

gt  gt  gt  a        gt  gt  gt  for i in xrange 3           a append             for j in xrange 3                   a i  append i j       gt  gt  gt  a   0  1  2    1  2  3    2  3  4    gt  gt  gt

User · Answer

If you want to do some serious work with arrays then you should use the numpy library  This will allow you for example to do vector addition and matrix multiplication  and for large arrays it is much faster than Python lists    However  numpy requires that the size is predefined  Of course you can also store numpy arrays in a list  like   import numpy as np vec list    np zeros  3    for   in range 10   vec list append np array  1 2 3    vec sum   vec list 0    vec list 1     possible because we use numpy print vec list 10  2     prints 3   But since your numpy arrays are pretty small I guess there is some overhead compared to using a tuple  It all depends on your priorities   See also this other question  which is pretty similar  apart from the variable size

[python] 2D arrays in Python

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