How to Extract Multiple JSON Objects from a Single File Efficiently Using Python\'s `json.JSONDecoder.raw_decode`?

Iteratively Extracting Multiple JSON Objects from a Single File

When dealing with JSON files containing multiple JSON objects, it's crucial to find an efficient way to extract specific data elements from each object.

One approach is to utilize Python's json.JSONDecoder.raw_decode function. This function allows you to decode large JSON strings containing multiple objects, even if they're not wrapped in a root array.

To begin, you'll need to strip any leading whitespace from the JSON document. Afterwards, you can use raw_decode in a loop to extract objects one by one. The function returns the last position where the parsed object ended and the object itself.

Here's a code snippet that demonstrates this approach:

<code class="python">from json import JSONDecoder, JSONDecodeError
import re

NOT_WHITESPACE = re.compile(r'\S')

def decode_stacked(document, pos=0, decoder=JSONDecoder()):
    while True:
        match = NOT_WHITESPACE.search(document, pos)
        if not match:
            return
        pos = match.start()

        try:
            obj, pos = decoder.raw_decode(document, pos)
        except JSONDecodeError:
            # handle error
            raise
        yield obj</code>

Using this method, you can decode a JSON string with multiple objects and extract specific elements into a data frame. For instance, if your JSON file contains the following structure:

<code class="json">{"ID":"12345","Timestamp":"20140101", "Usefulness":"Yes",
 "Code":[{"event1":"A","result":"1"},…]}
{"ID":"1A35B","Timestamp":"20140102", "Usefulness":"No",
 "Code":[{"event1":"B","result":"1"},…]}
{"ID":"AA356","Timestamp":"20140103", "Usefulness":"No",
 "Code":[{"event1":"B","result":"0"},…]}
…</code>

Your code could use the following loop to extract the "Timestamp" and "Usefulness" values:

<code class="python">import pandas as pd

data = []
for obj in decode_stacked(json_string):
    data.append([obj["Timestamp"], obj["Usefulness"]])

df = pd.DataFrame(data, columns=["Timestamp", "Usefulness"])</code>

This method provides a flexible and efficient way to extract multiple JSON objects from a single file, allowing you to gather data from complex JSON structures into a tabular format.

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