Fastest way to get values from dictionary to another dictionary in python without using if?

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I need to find a way to get values from one dictionary to another, bases on key name match without using two loops \ if statement.

Main goal is to make it run more efficiently since it's a part of a larger code and run on multiple threads.

If you can keep the dictionary structure it would help

The second dict is initialized with values 0 in advanced

dict_1 = {
    "school": {
        "main": ["first_key"]
    },
    "specific": {
        "students": [
            {
                "name": "sam",
                "age": 13
            },
            {
                "name": "dan",
                "age": 9
            },
            {
                "name": "david",
                "age": 20
            },
            {
                "name": "mike",
                "age": 5
            }
        ],
        "total_students": 4
    }
}

dict_2 = {'sam': 0, 'mike': 0, 'david': 0, 'dan': 0, 'total_students': 0}

for i in dict_1["specific"]['students']:
    for x in dict_2:
        if x == i["name"]:
            dict_2[x] = i["age"]

    dict_2["total_students"] = dict_1["specific"]["total_students"]

print(dict_2)

Is there more elegant way of doing it?

if-statement dictionary python loops
2 Answers

You don't need two loops at all! You don't even need to initialize dict_2 in advance. Simply loop over dict_1["specific"]["students"] and assign the ages to dict_2 without an if.

for student in dict_1["specific"]["students"]:
    student_name = student["name"]
    student_age = student["age"]
    dict_2[student_name] = student_age

You could also write this as a comprehension:

dict_2 = {student["name"]: student["age"] for student in dict_1["specific"]["students"]}

Both these give the following dict_2:

{'sam': 13, 'dan': 9, 'david': 20, 'mike': 5}

Then you can set dict_2["total_students"] like you already do, but outside any loops.

dict_2["total_students"] = dict_1["specific"]["total_students"]

If you only want to assign ages for students already in dict_2, you need the if. However, you can still do this with a single loop instead of two. :

for student in dict_1["specific"]["students"]:
    student_name = student["name"]
    if student_name not in dict_2:
        continue # skip the rest of this loop

    student_age = student["age"]
    dict_2[student_name] = student_age

Both these approaches use a single loop, so they're going to be faster than your two-loop approach.

user_8439530 
for i in dict_1['specific']['students']:
 dict_2[i['name']]=i['age']

dict_2['total_students']=dict_1['specific']['total_students']

Runs in O(N) time and O(N) space. Yours currently runs in O(N^2) time and O(N) space

user_120916890
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