Combining two lists which do not have same numbers of entries

Question

I have following two lists to combine. I'm trying to use zip() but header_list runs out for obvious reason.

header_list = ['1 mo', '3 mo', '6 mo', '1 yr', '2 yr', '3 yr', '5 yr', '7
yr', '10 yr', '20 yr', '30 yr']

data_list = [1.29, 1.44, 1.61, 1.83, 1.92, 2.01, 2.25, 2.38, 2.46,
2.64, 2.81, 1.29, 1.41, 1.59, 1.81, 1.94, 2.02, 2.25, 2.37, 2.44, 2.62, 2.78, 1.28, 1.41, 1.6, 1.82, 1.96, 2.05, 2.27, 2.38, 2.46, 2.62, 2.79]

The result should be a tuple in the following format:

('1 mo', 1.29)
('3 mo', 1.44)
('6 mo', 1.61)
('1 yr', 1.83)
('2 yr', 1.92)
('3 yr', 2.01)
('5 yr', 2.25)
('7 yr', 2.38)
('10 yr', 2.46)
('20 yr', 2.64)
('30 yr', 2.81)
('1 mo', 1.29)
('3 mo', 1.41)
('6 mo', 1.59)
('1 yr', 1.81)
('2 yr', 1.94)
('3 yr', 2.02)
('5 yr', 2.25)
('7 yr', 2.37)
('10 yr', 2.44)
('20 yr', 2.62)
('30 yr', 2.78)
...

Bailey Parker · Accepted Answer · 2018-01-20T01:23:01.137

6

If you use itertools you can use cycle to repeat the shorter one:

from itertools import cycle
print(zip(cycle(header_list), data_list))

zip will stop once the shorter iterable ends. cycle returns an iterable that never ends (constantly repeats header_list), so data_list will be shorter (and it will stop zipping when data_list ends).

edited Jan 20 '18 at 01:23

answered Jan 20 '18 at 01:21

Bailey Parker

15,599
5
53
91

I wasn't aware of the `cycle` function, thanks for this! – Niema Moshiri Jan 20 '18 at 01:22
Awesome, does the job. Thx a lot – Hannan Jan 20 '18 at 01:24

Niema Moshiri · Answer 2 · 2018-01-20T01:35:03.267

1

Assuming you want the shorter list to simply wrap, you can iterate over the indices of the longer list and mod the current index by the length of the shorter list:

out = [(header_list[i%len(header_list)], data_list[i]) for i in range(len(data_list))]

Or, to be more Pythonic:

out = [(header_list[i%len(header_list)], e) for i,e in enumerate(data_list)]

edited Jan 20 '18 at 01:35

answered Jan 20 '18 at 01:20

Niema Moshiri

909
5
14

Thanks, this work fine. – Hannan Jan 20 '18 at 01:24
Instead of iterating over `range(len(data_list))`, I'd contend the more python way would be to iterate over `enumerate(data_list)`. List indices are generally less pythonic. – Bailey Parker Jan 20 '18 at 01:28
@BaileyParker Thanks, added as an option – Niema Moshiri Jan 20 '18 at 01:35

score 0 · Answer 3 · answered Jan 20 '18 at 01:23

0

how about something like this?

counter = 0
new_list = []
for data in data_list:
    new_list.append([header_list[counter%len(header_list)],data])
    counter+=1

answered Jan 20 '18 at 01:23

oldlodestone

52
2

In general, using counters and `list.append` isn't very pythonic. In this instance, you'd definitely be better off constructing the list via a comprehension. If you do need to access an index, `enumerate` is your friend. – Bailey Parker Jan 20 '18 at 01:27
@BaileyParker `list.append` is *perfectly pythonic*, although you are correct, here `enumerate` is what you would use instead of a counter variable. Better yet, though, it would be `zip` – juanpa.arrivillaga Jan 20 '18 at 01:33

Combining two lists which do not have same numbers of entries

3 Answers3