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Created on 2009-04-27 12:10 by sjohn, last changed 2022-04-11 14:56 by admin. This issue is now closed.
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| File name | Uploaded | Description | Edit | |
| testsumflat.py | sjohn, 2009-04-27 12:10 | Performance check - test file (just execute) | ||
| Messages (2) | |||
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| msg86658 - (view) | Author: (sjohn) | Date: 2009-04-27 12:10 | |
To flatten lists of lists, e.g. [[0], [1], [2], ...], I found the short and quite python-like one-liner "sum(listoflists, [])". This, however, has absolutely awful performance: while the equivalent way of iterating by hand and extending a flat list is longer and uglier, it performs fast and in linear time. The sum() variant takes unacceptably long. I do not know why this should behave worse-than-linear... |
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| msg86659 - (view) | Author: Antoine Pitrou (pitrou) *  |
Date: 2009-04-27 12:38 | |
No wonder it's quadratic (rather than exponential), since summing will invoke the + operator and therefore produce a new list object at every iteration. If you use "f = f + l" in your explicit version, it becomes quadratic too. |
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| History | |||
|---|---|---|---|
| Date | User | Action | Args |
| 2022-04-11 14:56:48 | admin | set | github: 50105 |
| 2009-04-27 12:38:33 | pitrou | set | status: open -> closed nosy: + pitrou messages: + msg86659 resolution: not a bug |
| 2009-04-27 12:10:46 | sjohn | create | |