Python Split List by Filter

Directory 1. bifurcate2. enumerate3. List derivation

1. bifurcate

def bifurcate(lst, filter):
  return [
    [x for i, x in enumerate(lst) if filter[i] == True],
    [x for i, x in enumerate(lst) if filter[i] == False]
  ]

# EXAMPLES
bifurcate(['beep', 'boop', 'foo', 'bar'], [True, True, False, True]) # [ ['beep', 'boop', 'bar'], ['foo'] ]

bifurcate Function passes through a filter filter The input list lst is divided into two groups. Will filter Middle is True Corresponding to the lst Put the item in the first list of the results, and put the filter Middle is False The entry corresponding to lst of is placed in the second list of the results.

2. enumerate

enumerate(iterable, start=0)

enumerate The function receives 1 iterative object and returns 1 iterative object. The iterative object returns 1 tuple per iteration, and the tuple includes 1 sequence number and the iterative value of the received iterable object. start Parameter is used to set the initial value of the sequence number, which defaults to 0.

The example uses:

>>> seasons = ['Spring', 'Summer', 'Fall', 'Winter']
>>> list(enumerate(seasons))
[(0, 'Spring'), (1, 'Summer'), (2, 'Fall'), (3, 'Winter')]
>>> list(enumerate(seasons, start=1))
[(1, 'Spring'), (2, 'Summer'), (3, 'Fall'), (4, 'Winter')]

The implementation logic of the enumerate function is equivalent to the following code:

def enumerate(sequence, start=0):
    n = start
    for elem in sequence:
        yield n, elem
        n += 1

3. Table derivation

This function uses a list derivation to determine lst Of the position corresponding to the value inside filter And generate the corresponding grouping list.

A brief introduction to the list derivation can be seen: Python realizes filtering out the chapter of only 1 value in the list.