#0204

Train/Test Split by Time

MediumML25 min20 XP

Problem

Given rows sorted by date and a cutoff date, return train rows before cutoff and test rows on or after cutoff.

Why This Matters

Time-based leakage is one of the easiest ways to make a model look good offline and fail in production.

Function Signature

def split_by_cutoff(rows, cutoff):

Examples

Example 1

Input[2026-01-01, 2026-01-05, 2026-02-01], cutoff = 2026-02-01

Output2 train rows, 1 test row

Rows before February go to train; February 1 goes to test.

Constraints

Return the exact requested result.
Handle common edge cases.
Keep the solution readable before optimizing.

CodePython

def split_by_cutoff(rows, cutoff):
    """
    Input example: [2026-01-01, 2026-01-05, 2026-02-01], cutoff = 2026-02-01
    Return: 2 train rows, 1 test row
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return [], []

def split_by_cutoff(rows, cutoff):
    """
    Input example: [2026-01-01, 2026-01-05, 2026-02-01], cutoff = 2026-02-01
    Return: 2 train rows, 1 test row
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return [], []

Visible browser tests run here when available.

Testcases1 visible / 3 hidden categories

Core example

Input[2026-01-01, 2026-01-05, 2026-02-01], cutoff = 2026-02-01

Expected2 train rows, 1 test row

Rows before February go to train; February 1 goes to test.

Hidden Test Categories

empty or minimal inputrepeated valueslarger realistic input