Basic numeric runs
Input
[1, 1, 2, 2, 2, 3]
Output
[[1, 1], [2, 2, 2], [3]]
Two 1s form the first run, three 2s the second, and a single 3 the last.
Full lesson preview
Group equal consecutive values into sublists
Group runs of consecutive equal values in a list into sublists, preserving order and element types.
Python practice25 minLists & TuplesAdvancedLast updated March 17, 2026
Problem statement
Write a function group_consecutive(lst) that takes a list lst and returns a new list of lists. Each sublist should contain consecutive elements from lst that are equal to each other. The order of runs should match their order in the original list. If lst is empty, return an empty list. Elements can be of any type and equality should use Python's standard == operator.
Task
Given a list, return a list of sublists where each sublist contains a maximal consecutive run of equal values from the original list.
Examples
Different types and booleans
Input
[True, True, False, False, False]
Output
[[True, True], [False, False, False]]
Runs are formed using == equality; booleans group separately from other values.
Input format
A single argument: a list (possibly empty) of values.
Output format
Return a list of lists, where each inner list is a consecutive run of equal values.
Constraints
Do not use external libraries. Preserve the original element values and relative order. Time complexity should be O(n).
Samples
Sample 1
Input
["a", "a", "b", "b", "a"]
Output
[['a', 'a'], ['b', 'b'], ['a']]
The last 'a' is not consecutive with the first two, so it starts a new run.