Merge two keys of a single dictionary in python

Question

For a dictionary "a", with the keys "x, y and z" containing integer values. What is the most efficient way to produce a joint list if I want to merge two keys in the dictionary (considering the size of the keys are identical and the values are of interger type)?

x+y and y+z ? .

Explanation:

Suppose you have to merge two keys and merge them into a new list or new dict without altering original dictionaries.

Example:

a = {"x" : {1,2,3,....,50}
     "y" : {1,2,3,.....50}
     "z" : {1,2,3,.....50}
    }

Desired list:

x+y = [2,4,6,8.....,100]
y+z = [2,4,6,......,100]

Answer 1

A very efficient way is to do convert the dictionary to a pandas dataframe and allow it to do the job for you with its vectorized methods:

import pandas as pd

a = {"x" : range(1,51), "y" : range(1,51), "z" : range(1,51)}

df = pd.DataFrame(a)
x_plus_y = (df['x'] + df['y']).to_list()
y_plus_z = (df['y'] + df['z']).to_list()

print(x_plus_y)
#[2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100]

Answer 2

It seems like you're trying to mimic a join-type operation. That is not native to python dicts, so if you really want that type of functionality, I'd recommend looking at the pandas library.

If you just want to merge dict keys without more advanced features, this function should help:

from itertools import chain
from collections import Counter
from typing import Dict, List, Set, Tuple

def merge_keys(data: Dict[str, Set[int]], *merge_list: List[Tuple[str, str]]):
    merged_data = dict()
    merged_counts = Counter(list(chain(*map(lambda k: list(data.get(k, {})) if k in merge_list else [], data))))
    merged_data['+'.join(merge_list)] = [k*v for k,v in merged_counts.items()]
    return merged_data

You can run this with merge_keys(a, "x", "y", "z", ...), where a is the name of your dict- you can put as many keys as you want ("x", "y", "z", ...), since this function takes a variable number of arguments.

If you want two separate merges in the same dict, all you need to do is:

b = merge_keys(a, "x", "y") | merge_keys(a, "y", "z")

Note that the order of the keys changes the final merged key ("y+z" vs "z+y") but not the value of their merged sets.

P.S: This was actually a little tricky since the original dict had set values, not lists, which aren't ordered, so you can't just add them elementwise. That's why I used Counter here, in case you were wondering.