How to filter a JSON array in Python

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# How to filter a JSON array in Python

To filter a JSON array in Python:

Use the json.loads() method to convert the JSON array to a Python list.
Use a list comprehension to iterate over the list.
Check if each item in the list meets a certain condition and return the result.

main.py

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import json

json_array = json.dumps(
    [
        {'name': 'Alice', 'salary': 100},
        {'name': 'Bobby', 'salary': 50},
        {'name': 'Carl', 'salary': 75}
    ]
)

a_list = json.loads(json_array)

filtered_list = [
    dictionary for dictionary in a_list
    if dictionary['salary'] > 50
]

# 👇️ [{'name': 'Alice', 'salary': 100}, {'name': 'Carl', 'salary': 75}]
print(filtered_list)

filter json array

The code for this article is available on GitHub

The json.dumps() method converts a Python object to a JSON formatted string.

Conversely, the json.loads() method parses a JSON string into a native Python object.

We used the json.loads() method to convert the JSON array to a native Python list.

We then used a list comprehension to iterate over the list.

On each iteration, we check if a certain condition is met and return the result.

The code sample checks if each dictionary has a salary key with a value greater than 50.

main.py

Copied!
import json

json_array = json.dumps(
    [
        {'name': 'Alice', 'salary': 100},
        {'name': 'Bobby', 'salary': 50},
        {'name': 'Carl', 'salary': 75}
    ]
)

a_list = json.loads(json_array)

filtered_list = [
    dictionary for dictionary in a_list
    if dictionary['salary'] > 50
]

# 👇️ [{'name': 'Alice', 'salary': 100}, {'name': 'Carl', 'salary': 75}]
print(filtered_list)

The new list only contains the dictionaries that meet the condition.

You can use this approach to check for any condition.

Alternatively, you can use a for loop.

# How to filter a JSON array using a `for` loop

This is a four-step process:

Use the json.loads() method to convert the JSON array to a Python list.
Use a for loop to iterate over the list.
Check if each list item meets a certain condition.
Append the matching items to a new list.

main.py

Copied!
import json

json_array = json.dumps(
    [
        {'name': 'Alice', 'salary': 100},
        {'name': 'Bobby', 'salary': 50},
        {'name': 'Carl', 'salary': 75}
    ]
)

a_list = json.loads(json_array)

filtered_list = []

for dictionary in a_list:
    if dictionary['salary'] > 50:
        filtered_list.append(dictionary)

# 👇️ [{'name': 'Alice', 'salary': 100}, {'name': 'Carl', 'salary': 75}]
print(filtered_list)

filter json array using for loop

The code for this article is available on GitHub

We used a for loop to iterate over the list.

On each iteration, we check if the current dictionary has a salary key with a value greater than 50.

If the condition is met, we use the list.append() method to append the dictionary to a new list.

The list.append() method adds an item to the end of the list.

The new list only contains the items of the original list that meet the condition.

You can use the same approach to filter a JSON array stored in a file.

# Filter a JSON array that is stored in a file in Python

To filter a JSON array that is stored in a file:

Open the JSON file in reading mode.
Use the JSON.load() method to deserialize the file to a Python list.
Use a list comprehension to filter the list.

main.py

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import json

file_name = 'example.json'

with open(file_name, 'r', encoding='utf-8') as f:
    a_list = json.load(f)

    # 👇️ [{'name': 'Alice', 'salary': 100}, {'name': 'Bobby', 'salary': 50}, {'name': 'Carl', 'salary': 75}]
    print(a_list)

    filtered_list = [
        dictionary for dictionary in a_list
        if dictionary['salary'] > 50
    ]

    # 👇️ [{'name': 'Alice', 'salary': 100}, {'name': 'Carl', 'salary': 75}]
    print(filtered_list)

The code sample assumes that you have an example.json file stored in the same directory as your main.py script.

example.json

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[
  {"name": "Alice", "salary": 100},
  {"name": "Bobby", "salary": 50},
  {"name": "Carl", "salary": 75}
]

filter json array that is stored in file

The code for this article is available on GitHub

The json.load() method is used to deserialize a file to a Python object.

On the other hand, the json.loads() method is used to deserialize a JSON string to a Python object.

The json.load() method expects a text file or a binary file containing a JSON document that implements a .read() method.

Once we have the data from the JSON file parsed to a native Python list, we can use a list comprehension or a for loop to filter the list.

You can also use the filter() function to filter a JSON array.

# Filter a JSON array using the `filter()` function

This is a three-step process:

Use the json.loads() function to parse the JSON array into a Python list.
Pass a lambda function and the list to the filter() function.
The lambda function should check if each list item meets a condition.

main.py

Copied!
import json

json_array = json.dumps(
    [
        {'name': 'Alice', 'salary': 100},
        {'name': 'Bobby', 'salary': 50},
        {'name': 'Carl', 'salary': 75}
    ]
)

a_list = json.loads(json_array)

filtered_list = list(
    filter(
        lambda dictionary: dictionary['salary'] > 50,
        a_list
    )
)

# 👇️ [{'name': 'Alice', 'salary': 100}, {'name': 'Carl', 'salary': 75}]
print(filtered_list)

filter json array using filter function

The code for this article is available on GitHub

The filter() function takes a function and an iterable as arguments and constructs an iterator from the elements of the iterable for which the function returns a truthy value.

The lambda function we passed to filter() gets called with each dictionary from the list.

The function checks if the dictionary meets a certain condition and returns the result.

The last step is to use the list() class to convert the filter object to a list.

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How to filter a JSON array in Python

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