On 12/10/2022 08.32, SquidBits _ wrote:
Does anyone else think there should be a flatten () function, which just turns
a multi-dimensional list into a one-dimensional list in the order it's in. e.g.
[[1,2,3],[4,5,6,7],[8,9]] becomes [1,2,3,4,5,6,7,8,9].
I have had to flatten lists quite a few times and it's quite tedious to type
out. It feels like this should be something built in to python, anyone else
think this way?
There is a flatten function!
First though, are we ONLY talking about 'flattening' a 2D list (per
example, above) or might the requirements extend to multiple-dimensions?
The solutions vary accordingly!
Two-dimensions:
(don't think this method previously-mentioned, but very readable)
>>> l = [[1,2,3],[4,5,6,7],[8,9]]
>>> flattened = list()
>>> for element in l:
... flattened += element
...
>>> flattened
[1, 2, 3, 4, 5, 6, 7, 8, 9]
(NB if "l" were three-dimensional, "flattened" would become 2D)
Multi-dimensional:
Reach for itertools:
(https://docs.python.org/3/library/itertools.html#itertools.chain)
>>> import itertools as it
>>> iter_flattened = it.chain( *l )
>>> list( iter_flattened )
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Wrt "I have had to flatten lists quite a few times and it's quite
tedious to type out.", isn't this a "code-smell"?
Certainly motivation to generalise and write a solution as a function.
Do it once, and do it right!
Hence advice elsewhere to build a list-processing utility-library.
On the other hand, has it already been done for us?
An exercise for the reader:
is reaching for itertools 'over-kill' in 2D?
- speed-comparison between loading the itertools library and then
employing the speedy method, or using a (built-in) for-loop at
Python-speed with no import-overhead?
(results will vary significantly according to len( l ), but do they
remain consistently in-favor or one method or the other?)
--
Regards,
=dn
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