breaking a list in to lists in python?

Question

I have the following list of strings:

data = ["1","0","1","<>","0","1","0","<>","1","0","1"]

What I'd like as a result is:

[[1, 0, 1], [0, 1, 0], [1, 0, 1]]

E.g. a list of lists where each list is delimited by <> and the resultant strings converted to integers.

I don't see how this is a duplicate given that the chunks are not necessarily evenly-sized. — Andrew Magee, Mar 09 '15 at 10:14
@AndrewMagee: indeed, my mistake, reopened. The terrible formatting threw me off. — Martijn Pieters, Mar 09 '15 at 10:20

score 3 · Answer 1 · answered Mar 09 '15 at 10:22

3

You can use itertools.groupby to effectively partition at each <>, then take the resulting groups where the key isn't True (eg: it's a <>) and convert to ints, eg:

from itertools import groupby

data = ["1","0","1","<>","0","1","0","<>","1","0","1"]
new_date = [[int(i) for i in g] for k, g in groupby(data, '<>'.__ne__) if k]
# [[1, 0, 1], [0, 1, 0], [1, 0, 1]]

answered Mar 09 '15 at 10:22

Jon Clements

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I tested your code and being stopped by this error: invalid literal for int() with base 10: '<' – mahya.khazaee Mar 09 '15 at 10:39
@mahya.khazaee: you have fractions in your data? – Jerry Mar 09 '15 at 10:40
1

@mahya.khazaee so you have a single `<` in your data - eg - the sample you posted isn't representative of your actual data? What would you *expect* to happen for that? – Jon Clements Mar 09 '15 at 10:46

score 0 · Answer 2 · answered Mar 09 '15 at 10:45

0

I suggest you more functional-style solution:

data = ["1","0","1","<>","0","1","0","<>","1","0","1"]
reduce(lambda a, b: a[:-1] + [a[-1] + [int(b)]] if b != '<>' else a + [[]], data, [[]])

answered Mar 09 '15 at 10:45

shybovycha

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score 0 · Answer 3 · answered Mar 09 '15 at 11:15

You may try this also.

l = ["1","0","1","<>","0","1","0","<>","1","0","1"]
m = []
x = []
j = []
for i in l:
    if  i == '<>':
        m.append(x)
        x = []
        j = []
    else:
        x.append(int(i))
        j.append(int(i))
m.append(j)
print(m)

Output:

[[1, 0, 1], [0, 1, 0], [1, 0, 1]]

Malik Brahimi · Accepted Answer · 2015-03-09T10:46:43.650

-2

You can try using list comprehensions with a combination of joining and splitting:

your_list = [[int(j) for j in i.split()] for i in ' '.join(data).split('<>')]

edited Mar 09 '15 at 10:46

answered Mar 09 '15 at 10:41

Malik Brahimi

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That will fail the second the list has a number in it with more than one digit. – Andrew Magee Mar 09 '15 at 10:42
How will it differentiate `["1", "0", "<>", ...]` from `["10", "<>", ...]`? – Andrew Magee Mar 09 '15 at 10:44
I fixed it now, but the problem seemed to pertain only to ones and zeros. – Malik Brahimi Mar 09 '15 at 10:47
This may work, but *boy* is it an ugly approach, and a fragile one at that. – Martijn Pieters Mar 09 '15 at 13:31
@MartijnPieters How is it fragile? It works without any possibility of failure. – Malik Brahimi Mar 09 '15 at 16:05
It only works for input data that itself doesn't contain your chosen delimiter. You already had a sequence, why join then split again? You'd have to keep adjusting this approach for different inputs based on what data is contained. The `groupby` solution is far more robust in that it doesn't have to first destroy the input sequence. Also, your approach is very inefficient for large inputs; building a huge string then splitting it up is just a waste of memory and cycles. – Martijn Pieters Mar 09 '15 at 16:11

breaking a list in to lists in python?

4 Answers4