The Python Book

numpy magic sample_data
20141021

The magic matrices (a la octave).

 ```23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 ``` ``````magic3= np.array( [[8, 1, 6], [3, 5, 7], [4, 9, 2] ] ) magic4= np.array( [[16, 2, 3, 13], [ 5, 11, 10, 8], [ 9, 7, 6, 12], [ 4, 14, 15, 1]] ) magic5= np.array( [[17, 24, 1, 8, 15], [23, 5, 7, 14, 16], [ 4, 6, 13, 20, 22], [10, 12, 19, 21, 3], [11, 18, 25, 2, 9]] ) magic6= np.array( [[35, 1, 6, 26, 19, 24], [ 3, 32, 7, 21, 23, 25], [31, 9, 2, 22, 27, 20], [ 8, 28, 33, 17, 10, 15], [30, 5, 34, 12, 14, 16], [ 4, 36, 29, 13, 18, 11]] ) magic7= np.array( [ [30, 39, 48, 1, 10, 19, 28], [38, 47, 7, 9, 18, 27, 29], [46, 6, 8, 17, 26, 35, 37], [ 5, 14, 16, 25, 34, 36, 45], [13, 15, 24, 33, 42, 44, 4], [21, 23, 32, 41, 43, 3, 12], [22, 31, 40, 49, 2, 11, 20] ] ) # no_more_magic``````

Sum column-wise (ie add up the elements for each column):

``````np.sum(magic3,axis=0)
array([15, 15, 15])``````

Sum row-wise (ie add up elements for each row):

``````np.sum(magic3,axis=1)
array([15, 15, 15])``````

Okay, a magic matrix is maybe not the best way to show row/column wise sums. Consider this:

``````rc= np.array([[0, 1, 2, 3, 4, 5],
[0, 1, 2, 3, 4, 5],
[0, 1, 2, 3, 4, 5]])

np.sum(rc,axis=0)           # sum over rows
[0,  3,  6,  9, 12, 15]

np.sum(rc,axis=1)           # sum over columns
[15,
15,
15]

np.sum(rc)                  # sum every element
45``````

Notes by Willem Moors. Generated on momo:/home/willem/sync/20151223_datamungingninja/pythonbook at 2019-07-31 19:22