Python - Numpy array index as tuple

Question

If we create an array with Numpy , we can use many functionalities given by numpy library.

For example if c is a matrix

print(c[:,1])

will print every value in the column 1.

Now, when i index the c matrix in this way, am i indexing using a tuple ? If yes, how is possible to have a tuple with ':' inside ?

Are you asking how slicing works or how to have the ':' character in a tuple? — doctorlove
– doctorlove, Commented Jan 31, 2018 at 12:59
@doctorlove: I think Tantaros wants to understand how Numpy processes such slices internally. — willeM_ Van Onsem
– willeM_ Van Onsem, Commented Jan 31, 2018 at 13:03

willeM_ Van Onsem · Accepted Answer · 2018-01-31 13:02:14Z

2

The colon syntax is syntactical sugar for a slice(..) object. Your expression is equvalent to:

#        v slice object
print(c[(slice(None), 1)])
#       ^   tuple      ^

So you have passed a tuple containing a slice(None) object as first element, and 1 as second element.

The mapping of slice syntax to slice(..) objects is as follows:

Note that slice syntax is only supported in the context of an itemgetter (so x[..]).

answered Jan 31, 2018 at 13:02

willeM_ Van Onsem

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