CODEWITHSUNDEEP
python
Mauricio
Mauricio

Reputation: 3129

Python intersection inconsistent occurrence order

I'm trying to get a list of datetime separators of a string in the same order that they occur int it.

Suppose I have the following datetime: 2015-03-25 12:22:21; the output I intend to get from set().intersection is a list like this: ['-', ' ']

The problem is that it comes reversed. It seems random. Take a look at the following outputs:

[IN]: list(set('/|.-T ').intersection('2015-03-25 12:22:21'))
[OUT]: [' ', '-']

Now, this one comes correct:

[IN]: list(set('/|.-T ').intersection('2015-03-25T12:22:21'))`
[OUT]: ['-', 'T']

Why does the first one comes reversed with the space first? How can I approach this to get a consistent order?

Upvotes: 2

Views: 69

Answers (2)

PM 2Ring
PM 2Ring

Reputation: 55499

Here's a version that preserves the original order of the separators and doesn't output duplicate separators. When duplicates are present only the first one is included in the output.

def date_separators(datestring, seps):
    out = []
    for s in datestring:
        if s in seps and s not in out:
            out.append(s)
    return out

# test

data = (
    '2015-03-25 12:22:21',
    '2015-03-25T12:22:23',
    '5/6/2016 12:22:25 ',
)

seps = frozenset('/|.-T ')
for s in data:
    print(s, date_separators(s, seps))

output

2015-03-25 12:22:21 ['-', ' ']
2015-03-25T12:22:23 ['-', 'T']
5/6/2016 12:22:25  ['/', ' ']

Upvotes: 2

daemon24
daemon24

Reputation: 1448

set does not maintain order, You have to achieve it by looping

output = []
for i in '2015-03-25 12:22:21':
    if i not in output and i in '/|.-T ']:
        output.append(i)

Output:

['-', ' ']

Upvotes: 3

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