How do I add 2 elements for each iteration in a python shorthand list?

Question

I want to write a list like [i*2, i*3 for i in range(10)] so that I can have an output of [0, 0, 2, 3, 4, 6, 6, 9, 8, 12...] (so for each element in the range(10) I want to add 2 elements to the list from two calculations).

`[x for i in range(10) for x in (i * 2, i * 3)]`? Note it will also include two zeros. — jonrsharpe, May 11 '20 at 14:00
Why are the best answers always left as comments @jonrsharpe — Matthew Miles, May 11 '20 at 14:14

score 4 · Answer 1 · answered May 11 '20 at 14:01

4

Use itertools.chain.from_iterable, or any other Python iterable-flattening approach:

>>> list(itertools.chain.from_iterable([(i*2, i*3) for i in range(10)]))
[0, 0, 2, 3, 4, 6, 6, 9, 8, 12, 10, 15, 12, 18, 14, 21, 16, 24, 18, 27]

answered May 11 '20 at 14:01

blacksite

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Don't really need to pass as list: `list(itertools.chain.from_iterable((i*2, i*3) for i in range(10)))`. its fine to just pass a generator. – RoadRunner May 11 '20 at 14:22

ilyankou · Accepted Answer · 2020-05-11T14:04:56.227

2

Updated:

[ i*k for i in range(10) for k in (2, 3) ]

Original:

Just keeping it simple with list comprehension:

[ i*k for i in range(10) for k in range(2,4) ]

edited May 11 '20 at 14:04

answered May 11 '20 at 14:02

ilyankou

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score 1 · Answer 3 · answered May 11 '20 at 14:10

1

How about two for statements in a list comprehension?

[i*j for i in range(10) for j in [2, 3]]

answered May 11 '20 at 14:10

Oguz Incedalip

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Santhosh Reddy · Answer 4 · 2020-05-11T14:25:25.333

0

sum((map(lambda x: [x*2, x*3], range(10))), [])

output

[0, 0, 2, 3, 4, 6, 6, 9, 8, 12, 10, 15, 12, 18, 14, 21, 16, 24, 18, 27]

we can do it this way too, without any loops.

edited May 11 '20 at 14:25

answered May 11 '20 at 14:19

Santhosh Reddy

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I don't understand why my answer is irrelevant? can anyone please explain? – Santhosh Reddy May 11 '20 at 14:24
It's relevant but I gues it's less efficient than other answers... idk – Matthew Miles May 11 '20 at 15:01

How do I add 2 elements for each iteration in a python shorthand list?

4 Answers4