How to access the elements of a 2D array

Question

I would like to understand how one goes about manipulating the elements of a 2D array  If I have for example  a    a11 a12 a13    and b    b11 b12 b13        a21 a22 a23             b21 b22 b23  I have defined them in python as for example  a   1 1   2 1   3 1   b   1 2   2 2   3 2    I saw that I cannot refer to a 1  1  but to a 1  which gives me a result of  2 1   So  I don t understand how do I access the second row of these arrays  That would be a21  a22  a23  b21  b22  b23  And how would I do in order to multiply them as c1   a21 b21  c2   a22 b22  etc

User · Answer

If you want do many calculation with 2d array, you should use NumPy array instead of nest list.

for your question, you can use:zip(*a) to transpose it:

In [55]: a=[[1,1],[2,1],[3,1]]
In [56]: zip(*a)
Out[56]: [(1, 2, 3), (1, 1, 1)]
In [57]: zip(*a)[0]
Out[57]: (1, 2, 3)

User · Answer

If you have this    a     1  1    2  1   3  1     You can easily access this by using    print a 0  2   a 0  1    7 print a

User · Answer

If you have  a   1 1   2 1   3 1   b   1 2   2 2   3 2     Then  a 1  1    Will work fine  It points to the second column  second row just like you wanted   I m not sure what you did wrong   To multiply the cells in the third column you can just do  c    a 2  i    b 2  i  for i in range len a 2        Which will work for any number of rows   Edit  The first number is the column  the second number is the row  with your current layout  They are both numbered from zero  If you want to switch the order you can do  a   zip  a    or you can create it that way   a   1  2  3    1  1  1

User · Answer

a 1  1  does work as expected  Do you mean a11 as the first element of the first row  Cause that would be a 0  0

User · Answer

Look carefully how many brackets does your array have  I met an example when function returned answer with extra bracket  like that    gt  gt  gt approx array    1192   391             1191   409             1209   438             1191   409       And this didn t work   gt  gt  gt  approx 1 1  IndexError  index 1 is out of bounds for axis 1 with size 1   This could open the brackets    gt  gt  gt  approx   0  array   1192   391           1191   409           1209   438           1191   409      Now it is possible to use an ordinary element access notation     gt  gt  gt  approx   0  1 1  409

User · Answer

Seems to work here    gt  gt  gt  a   1 1   2 1   3 1    gt  gt  gt  a   1  1    2  1    3  1    gt  gt  gt  a 1   2  1   gt  gt  gt  a 1  0  2  gt  gt  gt  a 1  1  1

[python] How to access the elements of a 2D array?

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