Python quickest way to combine 2 list of dictionaries into one list of dictionary-CodePudding

ldict1 = [{"id":1, "name":"apple", "colour": "", "type": ""}, 
          {"id":2, "name":"orange", "colour": "", "type":""}]
ldict2 = [{"id":1, "colour":"red", "type":"fruit"}, 
          {"id":2, "colour":"orange", "type":"fruit"}]

Above is an example of the 2 types of list of dictionaries I want to merge. The id is the same for both. The length of both is long. I could only think of nested for loops but that could take time. What could be the quickest way to merge the same.

Expected

ldict = [{"id":1, "name":"apple", "colour": "red", "type": "fruit"}, 
         {"id":2, "name":"orange", "colour": "orange", "type":"fruit"}]

Note that the two lists always have the same order of id. Also, I want to add the missing details of ldict1 from ldict2. Those keys are always empty in ldict1 which need to be filled by ldict2.

CodePudding user response：

You could try with:

out = [{**i, **j} for i,j in zip(ldict1, ldict2)]

or if you have Python>=3.9:

out = [i | j for i,j in zip(ldict1, ldict2)]

Output:

[{'id': 1, 'name': 'apple', 'colour': 'red', 'type': 'fruit'},
 {'id': 2, 'name': 'orange', 'colour': 'orange', 'type': 'fruit'}]

Note that this works only if the ids match each pair of i-j. Also in the event that a key has values in both i and j, only the value from j is kept.

Also, (probably wouldn't be that different from a double loop but) if the ids don't match, we could use pandas module and use it's fillna method:

import pandas as pd
out = pd.DataFrame(ldict1).replace('', float('nan')).fillna(pd.DataFrame(ldict2)).to_dict('records')

CodePudding user response：

While the other answer meets the OP's need, here's one way to merge two dicts if we don't know which dict has to be updated:

# test data
ldict1 = [{"id":1, "name":"apple", "colour": "", "type": "fruit"}, 
          {"id":2, "name":"orange", "colour": "", "type":""}]
ldict2 = [{"id":1, "colour":"red", "type":""},  # type is missing here
          {"id":2, "colour":"orange", "type":"fruit"}]

[{k: i.get(k) or j.get(k) for k in {*i, *j}} for i, j in zip(ldict1, ldict2)]

Output:

[{'type': 'fruit', 'colour': 'red', 'id': 1, 'name': 'apple'},
 {'type': 'fruit', 'colour': 'orange', 'id': 2, 'name': 'orange'}]