find repeating dates between two datetime arrays python

Question

I have two datetime arrays, and I am trying to output an array with only those dates which are repeated between both arrays.. I feel like this is something I should be able to answer myself, but I have spent a lot of time searching and I do not understand how to solve this.

>>> datetime1[0:4]
array([datetime.datetime(2014, 6, 19, 4, 0), 
datetime.datetime(2014, 6, 19, 5, 0),
datetime.datetime(2014, 6, 19, 6, 0),
datetime.datetime(2014, 6, 19, 7, 0)], dtype=object)

>>> datetime2[0:4]
array([datetime.datetime(2014, 6, 19, 3, 0),
datetime.datetime(2014, 6, 19, 4, 0),
datetime.datetime(2014, 6, 19, 5, 0),
datetime.datetime(2014, 6, 19, 6, 0)], dtype=object)

I've tried this below but I still do not understand why this does not work

>>> np.where(datetime1==datetime2)
(array([], dtype=int64),)

John Zwinck · Accepted Answer · 2017-08-26 00:14:20Z

2

This:

datetime1==datetime2

Is an element-wise comparison. It compares [0] with [0], then [1] with [1], and gives you a boolean array.

Instead, try:

np.in1d(datetime1, datetime2)

This gives you a boolean array the same size as datetime1, set to True for those elements which exist in datetime2.

If your goal is only to get the values rather than the indexes, use this:

np.intersect1d(datetime1, datetime2)

https://docs.scipy.org/doc/numpy/reference/generated/numpy.intersect1d.html

answered Aug 26, 2017 at 0:14

John Zwinck

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Comments

cr1mson · Accepted Answer · 2017-08-26 00:13:22Z

2

I would say just iterate over the values of datetime1 and datetime2 and check for containment. So for example:

for date in datetime1:
    if date in datetime2:
        print(date)

edited Aug 26, 2017 at 0:13

answered Aug 26, 2017 at 0:12

cr1mson

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1 Comment

John Zwinck Over a year ago

For loops in NumPy are usually a poor solution.

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