Merge python list by specific indexes

January 16, 2022

I have an array, where I want a specific index to be merged.

["captain:", "robot", "alpha", "beta:", "gama", "delta:", "fighter", "test", "exp"]

the idea of this, every even element should contain : and the rest of the elements should not contain :

The output I want:

["captain:", "robot, alpha", "beta:", "gama", "delta:", "fighter, test, exp"]

considering the array is changeable, for example, the array could be:

["captain:", "robot", "beta:", "game", "exp", "delta:", "fighter", "test"]

the output should be the same, each even with : and odd index without :

Can anyone help, please?

>Solution :

Here’s an implementation using groupby:

import itertools
x = ["captain:", "robot", "alpha", "beta:", "gama", "delta:", "fighter", "test", "exp"]
new_list = []
for key, group in itertools.groupby(x, key = lambda string: string.endswith(':')):
    if key: # in case you happen to consecutive values that end in a colon
        new_list += list(group)
    else: # these elements do not end in a colon
        new_list.append(', '.join(group))
print(new_list)
# ['captain:', 'robot, alpha', 'beta:', 'gama', 'delta:', 'fighter, test, exp']

Here, the grouping key checks to see if the item ends in a ":", if it does, key is True, otherwise it is False. If consecutive values of key are the same, they are put in the same group. Thus, any number of elements following a string containing a colon will be grouped together.