Extract Filtered Events from JSON | Dataford Interview Questions

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Problem

Acme Analytics stores application logs as a large JSON payload. Write a function that parses the payload and extracts only the events that match a target event type and optional attribute filters.

Given a JSON string representing an object with an events array, return a list of simplified event objects for every valid event whose type matches target_type and whose key-value pairs in required_attrs are all present inside the event's attributes object.

Formal Specification

Implement:

payload: a JSON string
target_type: a string
required_attrs: a dictionary of required attribute filters

Return a list of dictionaries. Each output dictionary must contain:

id: event id
timestamp: event timestamp
user_id: user id if present, otherwise null

Ignore malformed event entries, events missing required top-level fields (id, type, timestamp), and events whose attributes field is not an object.

Constraints

1 <= len(events) <= 10^5
The JSON payload may be invalid; return an empty list in that case
Each valid event is a JSON object
Required top-level fields are id, type, and timestamp
required_attrs may be empty, in which case all events of the target type qualify

Function Signature

def extract_events(payload, target_type, required_attrs):