Combining nested lists according to first element

Question

So I have three lists:

lst1 = [('test1', 0.2), ('test7', 0.2)]
lst2 = [('test1', 5.2), ('test2', 11.1), ('test7', 0.2)]
lst3 = [('test1', 19.2), ('test2', 12.1), ('test7', 19.2), ('test9', 15.1)]

What I want to do is to go through the lists and create the following tuple:

[(test1, 0.2, 5.2, 19.2), (test2, 0.0, 11.1, 12.1), (test7, 0.2, 0.2, 19.2), (test9, 0.0, 0.0, 15.1)]

I have tried to solve this through multiple methods but no luck, any help is welcomed!

Answer 1

If you really want to use test1 etc. as unique keys, you might be better off using a dictionary.

I'd recommend the following: Use itertools.chain to combine the lists that you want to iterate over, and use a default dictionary that you simply append items to.

import itertools as it
from collections import defaultdict

lst1 = [('test1', 0.2), ('test7', 0.2)]
lst2 = [('test1', 5.2), ('test2', 11.1), ('test7', 0.2)]
lst3 = [('test1', 19.2), ('test2', 12.1), ('test7', 19.2), ('test9', 15.1)]


mydict = defaultdict(list)

for key, value in it.chain(lst1, lst2, lst3):
  mydict[key].append(value)

print(mydict)

> defaultdict(
        <class 'list'>,
        {'test1': [0.2, 5.2, 19.2],
        'test7': [0.2, 0.2, 19.2],
        'test2': [11.1, 12.1],
        'test9': [15.1]}
)