How do you extract nested values from a complex JSON structure?

Extracting Nested JSON Values

Problem:

When parsing JSON data, you may encounter complex and nested structures like this one:

<code class="json">{'name': 'ns1:timeSeriesResponseType',
 'declaredType': 'org.cuahsi.waterml.TimeSeriesResponseType',
 'scope': 'javax.xml.bind.JAXBElement$GlobalScope',
 'value': {'queryInfo': {'creationTime': 1349724919000,
                          'queryURL': 'http://waterservices.usgs.gov/nwis/iv/',
                          'criteria': {'locationParam': '[ALL:103232434]',
                                       'variableParam': '[00060, 00065]'},
                          'note': [{'value': '[ALL:103232434]',
                                    'title': 'filter:sites'},
                                   {'value': '[mode=LATEST, modifiedSince=null]',
                                    'title': 'filter:timeRange'},
                                   {'value': 'sdas01', 'title': 'server'}]}},
 'nil': False, 'globalScope': True, 'typeSubstituted': False}</code>

You want to extract a specific value, such as the 'creationTime' field.

Solution:

1. Navigate the Data Structure:

To extract the 'creationTime' value, we need to navigate the nested structure using keys:

<code class="python">my_dict['key1']['key2']['key3']</code>

2. Example Code:

To obtain the 'creationTime' value, use the following code:

<code class="python">creation_time = my_dict['value']['queryInfo']['creationTime']</code>

3. Determining the Path to Data:

To determine the path to a specific data element, examine the structure of the JSON response:

• Each key-value pair in the JSON structure represents a path segment.
• To access a nested value, simply concatenate the path segments with '[]'.

4. More General Approach:

If you encounter an unknown nested JSON structure, you can use a recursive function to navigate and retrieve the desired value:

<code class="python">def get_nested_value(data, path):
  if isinstance(data, dict):
    if path[0] in data:
      return get_nested_value(data[path[0]], path[1:])
    else:
      return None  # Raise an error if the key doesn't exist

  elif isinstance(data, list):
    if len(path) == 0:
      return data
    else:
      return get_nested_value(data[path[0]], path[1:])

  else:
    return data

value = get_nested_value(my_dict, ['value', 'queryInfo', 'creationTime'])</code>

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