CODEWITHSUNDEEP
pythonsumnested-lists
Akael
Akael

Reputation: 61

Sum a Nested List with condition in python

In order to simplify the reading of information for all other users, I would like to reduce a nested list where names appear in duplicate. Concrete example:

[['savoielibrercgcm', '0.25'], ['MeriFer', '0.25'], ['XlassII', '0.25'], ['Tomixt_31', '0.25'], ['Tomixt_31', '0.25'], ['Tomixt_31', '0.25']]

(The value is not always equal to 0.25)

The ideal would be to be able to add the content according to the nickname to obtain a list like this:

[['savoielibrercgcm', '0.25'], ['MeriFer', '0.25'], ['XlassII', '0.25'], ['Tomixt_31', '0.75']]

I could easily do it with a for loop and an if condition. But the program being heavy and having to manage data in great quantity, I would like to be able to "optimize" this code. I tried to go through a conversion to dict but that removes duplicate keys.

Do you have any ideas ? of the map? I must admit that I have never touched the map() :/

Thanks in advance for the help ^^'

Upvotes: 1

Views: 403

Answers (3)

Adon Bilivit
Adon Bilivit

Reputation: 26998

You could do this using an intermediate dictionary like this:

from collections import defaultdict

mydict = defaultdict(int)
mylist = [['savoielibrercgcm', '0.25'], ['MeriFer', '0.25'], ['XlassII', '0.25'], ['Tomixt_31', '0.25'], ['Tomixt_31', '0.25'], ['Tomixt_31', '0.25']]
for name, value in mylist:
    mydict[name] += float(value)
newlist = [[k, f'{v:.2f}'] for k, v in mydict.items()]
print(newlist)

Output:

[['savoielibrercgcm', '0.25'], ['MeriFer', '0.25'], ['XlassII', '0.25'], ['Tomixt_31', '0.75']]

Upvotes: 0

Alain T.
Alain T.

Reputation: 42143

Using an dictionary to group the names should work for this:

L = [['savoielibrercgcm', 0.25], ['MeriFer', 0.25], ['XlassII', 0.25],
     ['Tomixt_31', 0.25], ['Tomixt_31', 0.25], ['Tomixt_31', 0.25]]

grouped = dict()
grouped.update((name,grouped.get(name,0)+value) for name,value in L)
L = [*map(list,grouped.items())]

print(L)
[['savoielibrercgcm', 0.25], ['MeriFer', 0.25], ['XlassII', 0.25], 
 ['Tomixt_31', 0.75]]

Note: I assumed you don't really want your numerical values to be stored as strings

Upvotes: 0

mwo
mwo

Reputation: 456

Here's a solution using collections.Counter:

from collections import Counter

c = Counter()
for name, value in inputs:
    c[name] += float(value)

then you can convert the accumulated values for the name to string again. Counter works just like the built-in dict. I'm not sure if your task can be accomplished in a more performant way.

Upvotes: 1

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