Build a CSV Query Engine

Problem Statement

You are tasked with building a lightweight in-memory CSV query engine. The CSV file is provided as a string where rows are separated by newlines and columns are separated by commas. The first row contains headers.

Your task is to implement a QueryEngine class that performs the following:

1. Parsing & Inference: Convert the CSV string into an internal representation. Values that consist entirely of digits (optionally with a decimal point) should be treated as numbers; otherwise, keep them as strings.
2. Filter Method: Implement a filter(column_name, operator, value) method that returns a list of rows matching the condition.

Function Signature

class QueryEngine:
    def __init__(self, csv_data: str):
        # Parses the CSV and stores it internally
        pass

    def filter(self, col_name: str, operator: str, value: str) -> List[List[Any]]:
        # Filters rows based on the condition
        pass

Constraints

• Operators include: ==, !=, >, =, <=.
• If the column value and the input value are both numeric, perform numeric comparison. Otherwise, perform lexicographical comparison.
• Headers are unique.

Example

data = "name,age\nAlice,25\nBob,30"
engine = QueryEngine(data)

# Numeric comparison (25 > 20)
engine.filter("age", ">", "20") 
# Returns [['Alice', 25], ['Bob', 30]]

# String comparison
engine.filter("name", "==", "Alice") 
# Returns [['Alice', 25]]

Edge Cases

• Empty CSV input.
• Numeric values being compared as strings due to parsing errors.
• Columns that do not exist in the header.