finding unique numbers in array python code example

Example 1: return position of a unique value in python array

In [304]: array = np.array([1, 1, 2, 3, 2, 1, 2, 3])

In [305]: np.unique(array)            # unique values in `array`
Out[305]: array([1, 2, 3])

In [306]: array == 1                  # retrieve a boolean mask where elements are equal to 1
Out[306]: array([ True,  True, False, False, False,  True, False, False])

In [307]: (array == 1).nonzero()[0]   # get the `True` indices for the operation above
Out[307]: array([0, 1, 5])

Example 2: count unique values in python

words = ['a', 'b', 'c', 'a']
unique_words = set(words)             # == set(['a', 'b', 'c'])
unique_word_count = len(unique_words) # == 3