CODEWITHSUNDEEP
pythonlistsplit
cbros2008
cbros2008

Reputation: 353

Python: how to split a list into an unknown number of smaller lists based on a delimeter

I've got a list which contains the following strings:

MainList
'00:00'
'00:01'
'00:02'
'00:03'
'00:04'
'00:00'
'00:01'
'00:02'
'00:03'
'00:04'

I would like to split this into a smaller number of lists whenever '00:00' is encountered since '00:00' is the only element that won't change:

Desired output:
List1
'00:00'
'00:01'
'00:02'
'00:03'
'00:04'

List2
'00:00'
'00:01'
'00:02'
'00:03'
'00:04'

I tried looking at list slicing but the problem is that the last value and as such, number of elements may change. Moreover, I'm not sure how many smaller lists I'll need (and how I'd dynamically create n number of smaller lists?)

Upvotes: 2

Views: 2427

Answers (4)

Jochen Ritzel
Jochen Ritzel

Reputation: 107746

I usually do this:

def splitby( lst, breaker='00:00'):
    current = []
    it = iter(lst)
    first = next(it)
    assert first==breaker, "`lst` must begin with `breaker`"
    current.append(first)
    for item in it:
        if item == breaker:
            yield current
            current = []
        current.append(item)
    yield current

The inevitable itertools solution is a bit more general:

from itertools import groupby

class splitter(object):
    
    def __init__(self, breaker):
        self.breaker = breaker
        self.current_group = 0
        
    def __call__(self, item):
        if item == self.breaker:
            self.current_group+=1
        return self.current_group
        
    def group(self, items):
        return (list(v) for k,v in groupby(items,self))
    
print list(splitter('00:00').group(items))

Upvotes: 6

thiruvenkadam
thiruvenkadam

Reputation: 4260

I could think of another way :-)

def list_split(a):
    #a=['00:00', '00:01', '00:02', '00:03', '00:00', '00:01', '00:02']
    output = []
    count = 0

    if len(a) < 1:
        output.append(a)
        return output

    for i, item in enumerate(a[1:]):
        if item == a[0]:
            output.append(a[count:i+1])
            count = i + 1
    else:
        output.append(a[count:])
        return output

Upvotes: 0

utdemir
utdemir

Reputation: 27256

Comprehensions is your best friend :). Just two lines:

>>> a=['00:00', '00:01', '00:02', '00:03', '00:00', '00:01', '00:02']
>>> found=[index for index,item in enumerate(a) if item=='00:00'] + [len(a)]
>>> [a[found[i]:found[i+1]] for i in range(len(found)-1)]
[['00:00', '00:01', '00:02', '00:03'], ['00:00', '00:01', '00:02']]

Here is what we do:

We search for delimiter positions and get a list which contains delimiter indexes:

>>> found=[index for index,item in enumerate(a) if item=='00:00']
>>> found
[0, 4]

We're adding len(a) for including the last dict.

And creating new lists with splitting a with founded indexes :

>>> [a[found[i]:found[i+1]] for i in range(len(found)-1)]
[['00:00', '00:01', '00:02', '00:03'], ['00:00', '00:01', '00:02']]

Upvotes: 2

C&#233;dric Julien
C&#233;dric Julien

Reputation: 80851

In an explicit way, you could do like this : 

sep = '00:00'
split_list = []
for item in Mainlist:
    if item == sep:
        split_list.append([item])
    else:
        split_list[-1].append(item)

print split_list

Upvotes: 3

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