Change long python list with different layer with uniform one

Question

I have one long list such as:

m=[[["a", "b"],["c","d"]],[["1", "2"],["3","4"]]]

How could I change it into one list as:

[["a", "b"],["c","d"],["1", "2"],["3","4"]]

score 2 · Accepted Answer · answered Oct 15 '18 at 16:41

2

You can use nested list comprehension:

[s for l in m for s in l]

With your sample input, this returns:

[['a', 'b'], ['c', 'd'], ['1', '2'], ['3', '4']]

answered Oct 15 '18 at 16:41

blhsing

2

or even just `sum(m, [])` – Sam Mason Oct 15 '18 at 16:44
Really thx! It works. – Thomas.Q Oct 15 '18 at 16:46
1

@SamMason While concise, using `sum` is inefficient since for each add operation that joins two sublists there would be a new list created. – blhsing Oct 15 '18 at 17:00
@blhsing good point! another version is `l = []; for a in m: l.extend(a)` which is generally faster than your solution, but isn't a nice single line – Sam Mason Oct 15 '18 at 17:24

1 Answers1