I wish to know an efficient way and code saving to slice a list of thousand of elements
example:
b = ["a","b","c","d","e","f","g","h"]
index = [1,3,6,7]
I wish a result like as:
c = ["b","d","g","h"]
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Almost the same question with more solutions: Python List Slicing with Arbitrary Indicespabouk - Ukraine stay strong– pabouk - Ukraine stay strong2022-04-10 15:19:09 +00:00Commented Apr 10, 2022 at 15:19
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1 Answer
The most direct way to do this with lists is to use a list comprehension:
c = [b[i] for i in index]
But, depending on exactly what your data looks like and what else you need to do with it, you could use numpy arrays - in which case:
c = b[index]
would do what you want, and would avoid the potential memory overhead for large slices - numpy arrays are stored more efficiently than lists, and slicing takes a view into the array rather than making a partial copy.
3 Comments
Gianni Spear
thanks lvc I have this error message c = b[index] Traceback (most recent call last): File "<interactive input>", line 1, in <module> TypeError: list indices must be integers, not list
lvc
@Gianni as I said in my answer, that will work if you use numpy arrays instead of lists. They can take all kinds of interesting things as indexes; lists can only take integers (and slices with integer arguments).
Roland Smith
+1 for using a list comprehension. It's a good thing to teach newbies.