Numpy how to iterate over columns of array

Question

Suppose I have and m x n array   I want to pass each column of this array to a function to perform some operation on the entire column   How do I iterate over the columns of the array   For example  I have a 4 x 3 array like  1  99 2 2  14 5 3  12 7 4  43 1  for column in array    some function column    where column would be  1 2 3 4  in the first iteration   99 14 12 43  in the second  and  2 5 7 1  in the third

User · Answer

This should give you a start   gt  gt  gt  for col in range arr shape 1        some function arr   col      1 2 3 4   99 14 12 43   2 5 7 1

User · Answer

Alternatively  you can use enumerate  It gives you the column number and the column values as well    for num  column in enumerate array T       some function column    column  Gives you the column value as asked in the question     some function num    num  Gives you the column number

User · Answer

Just iterate over the transposed of your array   for column in array T     some function column

User · Answer

For example you want to find a mean of each column in matrix  Let s create the following matrix  mat2   np array  1 5 6 7 3 0 3 5 9 10 8 0   dtype np float64  reshape 3  4    The function for mean is  def my mean x       return sum x  len x    To do what is needed and store result in colon vector  results   results   np zeros 4  for i in range 0  4       mat2    i    my mean mat2    i    results   mat2 1            The results are   array  4 33333333  5           5 66666667  4

User · Answer

for c in np hsplit array  array shape 1        some fun c

User · Answer

You can also use unzip to iterate through the columns  for col in zip  array      some function col

User · Answer

For a three dimensional array you could try   for c in array transpose 1  0  2       do stuff c    See the docs on how array transpose works  Basically you are specifying which dimension to shift  In this case we are shifting the second dimension  e g  columns  to the first dimension

[python] Numpy how to iterate over columns of array?

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