Grouping elements into a list

July 21, 2022

I want to group elements into a list of list based on the indexing
Starting with the first position in data, go until the next False. That’s a grouping. Continue until the last element.

data = ['a','b','c','d','e','f'] 
indexer = [True, True, False, False, True, True]

Outcome would be:

[['a','b','c'], ['d'], ['e','f'] ]

Is itertools groupby the right solution? I’m a little confused about how to implement it.

>Solution :

You can simply append values to a temporary list and when you reach a False, create a new temporary list, first appending the last one to the resulting list, so basically, create a list after each False, lastly if necessary append the last temporary list to the result:

data = ['a', 'b', 'c', 'd', 'e', 'f']
indexer = [True, True, False, False, True, True]

result, temp = [], []
for value, index in zip(data, indexer):
    temp.append(value)
    if not index:
        result.append(temp)
        temp = []
if temp:
    result.append(temp)

print(result)
# [['a', 'b', 'c'], ['d'], ['e', 'f']]