advanced patterns when using `itertools.groupby` in Python 2.7 with non-sorted input
I'm getting frustrated with I'm not sure how to approach I've been struggling with this for a few days now and could really use some help..... I'm working with an scenario with `itertools.groupby()` in Python 2.7 when I use it on a list that isn't sorted. I expected it to group adjacent identical elements, but it seems to be missing some groups or returning empty results. Here's the code I've written so far: ```python import itertools data = [1, 2, 2, 1, 3, 2, 1] result = [list(group) for key, group in itertools.groupby(data)] print(result) ``` The output I receive is `[[1], [2, 2], [1], [3], [2], [1]]`, which is not what I wanted. I thought `groupby` would group all identical elements together regardless of their order in the list. After reading the documentation, it seems like `groupby` only groups consecutive identical elements. To address this, I tried sorting the data first: ```python data.sort() result = [list(group) for key, group in itertools.groupby(data)] print(result) ``` However, this leads to a different set of groups: `[[1, 1, 1], [2, 2], [3]]`. This approach works, but I’m concerned about the performance implications of sorting a large dataset. What’s the best practice to achieve what I want without losing performance? Should I be using a different method altogether, or is there a more efficient way to group elements without sorting the entire list? Any advice or suggestions would be greatly appreciated! My development environment is Windows. Any help would be greatly appreciated! I recently upgraded to Python latest. I'm working with Python in a Docker container on Ubuntu 22.04. I'd really appreciate any guidance on this. I'm working with Python in a Docker container on Windows 10.