#0001

Remove Duplicates Without Losing Order

EasyPython10 min10 XP

Problem

Given a list of values, return a new list that contains each value only once, keeping the order of first appearance.

Why This Matters

This tiny problem tests whether you understand the difference between a set as a membership helper and a list as an ordered result.

Function Signature

def unique_in_order(items):

Examples

Example 1

Inputitems = ["ml", "sql", "ml", "python", "sql"]

Output["ml", "sql", "python"]

"ml" and "sql" repeat later, but only their first appearances are kept.

Constraints

The input list can be empty.
Items are hashable values such as strings, numbers, or tuples.
Do not sort the result.

CodePython

def unique_in_order(items):
    """
    Input example: items = ["ml", "sql", "ml", "python", "sql"]
    Return: ["ml", "sql", "python"]
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    result = []
    # write your code here
    return result

def unique_in_order(items):
    """
    Input example: items = ["ml", "sql", "ml", "python", "sql"]
    Return: ["ml", "sql", "python"]
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    result = []
    # write your code here
    return result

Visible browser tests run here when available.

Testcases2 visible / 4 hidden categories

Mixed repeated strings

Input["ml", "sql", "ml", "python", "sql"]

Expected["ml", "sql", "python"]

The output keeps the first "ml", first "sql", and then "python".

Already unique

Input[3, 1, 4]

Expected[3, 1, 4]

Nothing is removed because no value repeats.

Hidden Test Categories

Empty listAll values repeatedNumbers mixed with negative valuesValues that would change order if sorted