从 JSON 文件中的字典列表返回值

Question

I have a JSON file and it has a list of dictionaries.I want to return only the subjects that are grater than 5.The JSON file is:

{
    "email":"mortonfitzgerald@ontagene.com",
    "courses": [
        {"CS": 10},
        {"Maths": 3},
        {"Data Analysis": 9},
        {"Java":4},
        {"C":8}
    ]
}

Desired output is:

["CS:10 ...

Answer 1

You can use the Python JSON module to parse the JSON into an object. Then you can filter the list based on that object.

import json

with open('data.json', 'r') as json_file:
    # parse string and get the courses part
    courses = json.loads(json_file.read())['courses']

    # convert single-entry dictionaries to tuples
    courses = [list(course.items())[0] for course in courses]

    # filter the courses based on the condition
    filtered_courses = list(filter(lambda course: course[1] > 5, courses))

    # prints [('CS', 10), ('Data Analysis', 9), ('C', 8)]
    print(filtered_courses)
    # prints {'CS': 10, 'Data Analysis': 9, 'C': 8}
    print(dict(filtered_courses))

Answer 2

Here is another way to do it without array filter using for loop:

import json

# this is the raw JSON loaded from a file
JSON = """
{
    "email":"mortonfitzgerald@ontagene.com",
    "courses": [
        {"CS": 10},
        {"Maths": 3},
        {"Data Analysis": 9},
        {"Java":4},
        {"C":8}
    ]
}
"""
# Loading coureses as json object
courses_json = json.loads(JSON)
# Selecting the courses list
courses = courses_json['courses']

# Empty list which will be populated by the filtered courses
filtered_courses = []

for index in range(len(courses)):
    for key in courses[index]:
        if courses[index][key] > 5:
            filtered_courses.append(key)

print(filtered_courses)

Answer 3

If you okay with a bit complex logic and are searching for shortcodes, I would suggest using a map and filter. This will make your code a lot shorter and optimized. For your reference I am attaching a small piece of code for your case:-

details =  {
    "email":"mortonfitzgerald@ontagene.com",
    "courses": [
        {"CS": 10},
        {"Maths": 3},
        {"Data Analysis": 9},
        {"Java":4},
        {"C":8}
    ]
}
values = list(map(lambda x: x[0],list(filter(lambda x: len(x) > 0, [list(filter(lambda key: d[key] > 5, d.keys())) for d in details["courses"]]))))

print(values)  --> ['CS', 'Data Analysis', 'C']

For a simple understanding, I am breaking the above one-liner code into chunks to give a brief overview of the power of map and filter function in python.

1. [list(filter(lambda key: d[key] > 5, d.keys())) for d in details["courses"]]

   As every entry inside details["courses"] is a dictionary key, value pair. I am using list comprehension to iterate the pair.

   " d " is those individual pairs. Then using the.keys() function I am trying to filter the " d " with a key whose value is greater than 5. This will return us a list of list of dictionary values. Because of which the pair which doesn't satisfy the condition will have an empty list inside the result. To understand it better, I have attached the output of this command

res = [list(filter(lambda key: d[key] > 5, d.keys())) for d in details["courses"]]

print(res)

[['CS'], [], ['Data Analysis'], [], ['C']]

2. Filtering out the empty list from the above output (res) " lambda x: len(x) > 0 " --> This lambda function will help in filtering out the list with size 0

filteredOutEmptyList = list(filter(lambda x: len(x) > 0, res))

print(filteredOutEmptyList)

3. Now you just have to run a mapper function to pull out the first element of each list.

finalOutput = list(map(lambda x: x[0], filteredOutEmptyList))

print(finalOutput)

There are lot more things and ways you can write the code using the map and filter function. It's very useful when dealing with iterable objects like lists, dictionaries, etc.

Please reach out in the comments if you need any further clarification, I will try my best to help you out.