CODEWITHSUNDEEP
pythonnumpy
user308827
user308827

Reputation: 22031

Subset numpy array based on another array

I have 2 numpy arrays:

arr_a = array(['1m_nd', '2m_nd', '1m_4wk'],
      dtype='<U15')

arr_b = array([0, 1, 1])

I want to select elements from arr_a based on arr_b. I am doing this: arr_a[arr_b], but I get this as result: 

array(['1m_nd', '2m_nd', '2m_nd'],
      dtype='<U15')

instead of:

array(['2m_nd', '1m_4wk'],
      dtype='<U15')

How do i fix this?

Upvotes: 4

Views: 7154

Answers (2)

Sudheesh Singanamalla
Sudheesh Singanamalla

Reputation: 2297

Given arr_a and arr_b, Running the following will give the boolean array for each of the elements in arr_b whose value is 1 => True and 0 => False . Correspondingly the boolean values are checked with the index value in arr_a. Here is the line of code you'd need.

>>> arr_a[arr_b == 1]
array([u'2m_nd', u'1m_4wk'],
      dtype='<U15')

Upvotes: 0

mrip
mrip

Reputation: 15163

You need to pass it a boolean array, for example:

>>> arr_a[arr_b>0]

array(['2m_nd', '1m_4wk'], 
      dtype='<U15')

Upvotes: 8

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