Searching

NumPy has several functions that can search through arrays, as follows:

• The argmax function gives the indices of the maximum values of an array.

  >>> a = np.array([2, 4, 8])
  >>> np.argmax(a)
  2
  

• The nanargmax function does the same but ignores NaN values.

  >>> b = np.array([np.nan, 2, 4])
  >>> np.nanargmax(b)
  2
  

• The argmin and nanargmin functions provide similar functionality but pertaining to minimum values.

• The argwhere function searches for non-zero values and returns the corresponding indices grouped by element.

  >>> a = np.array([2, 4, 8])
  >>> np.argwhere(a <= 4)
  array([[0],
         [1]])
  

• The searchsorted function tells you the index in an array where a specified value could be inserted to maintain the sort order. It uses binary search, which is a O(log n) algorithm. We will see this function in action shortly.

• The extract function retrieves values from an array based on a condition.