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MongoDB

Skip the first 2 documents from the `logs` collection using an aggregation pipeline.

Problem Statement

<p>Skip the first 2 documents from the <code>logs</code> collection using an aggregation pipeline.</p>

Examples

Input: logs collection: +-----+----------+ | _id | msg | +-----+----------+ | 1 | start | | 2 | process | | 3 | complete | | 4 | end | +-----+----------+

Output: +-----+----------+ | _id | msg | +-----+----------+ | 3 | complete | | 4 | end | +-----+----------+

Explanation: The query restricts and skips documents to return the specified subset.

Complexity

Time Complexity: -

Space Complexity: -

Hints

šŸ’” Hint 1: Use db.<collection>.aggregate([ ... ]) to run a multi-stage data processing pipeline. šŸ’” Hint 2: Order pipeline stages logically (e.g. $match early to filter documents before processing). šŸ’” Hint 3: Convert the aggregation cursor using .toArray() at the end of the function.

Editorial & Approach

Problem Overview & Intuition

To solve "Aggregation: $skip Stage", we query the MongoDB document store. The goal is to skip the first 2 documents from the `logs` collection using an aggregation pipeline. Using an aggregation pipeline, the database engine filters and structures the BSON documents efficiently.

Step-by-Step Approach

  1. Identify Target Collection: Access the collection through the db instance.
  2. Construct Query / Pipeline: Build the aggregation stages ($match, $group, $sort, etc.).
  3. Resolve Cursor: Invoke .toArray() to transform the query cursor into the required array of documents.

Optimal Implementation (MongoDB)

function solve(db) {
  return db.logs.aggregate([{ $skip: 2 }]);
}

Complexity Analysis

Time Complexity O(N) pipeline traversal through aggregation stages.
Space Complexity O(M) intermediate document buffer in aggregation pipeline.

Key Considerations & Edge Cases

  • Empty Collections: If no documents match, the query cleanly returns an empty array [].
  • Missing / NULL Fields: Missing fields in documents are handled safely without throwing runtime exceptions.
  • Type Coercion: BSON types (ObjectId, Numbers, Strings) are compared strictly according to MongoDB specifications.

Aggregation: $skip Stage

Medium

Skip the first 2 documents from the logs collection using an aggregation pipeline.

Example Scenarios
1Example 1
Input:
logs collection
_idmsg
1start
2process
3complete
4end
Output:
_idmsg
3complete
4end
Explanation:

The query restricts and skips documents to return the specified subset.

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Query Results (JSON)

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