CODEWITHSUNDEEP
python
ScientiaEtVeritas
ScientiaEtVeritas

Reputation: 5278

Split List By Value and Keep Separators

I have a list called list_of_strings that looks like this:

['a', 'b', 'c', 'a', 'd', 'c', 'e']

I want to split this list by a value (in this case c). I also want to keep c in the resulting split.

So the expected result is:

[['a', 'b', 'c'], ['a', 'd', 'c'], ['e']]]

Any easy way to do this?

Upvotes: 8

Views: 6468

Answers (8)

pylang
pylang

Reputation: 44515

You can use more_itertoools+ to accomplish this simply and clearly:

from more_itertools import split_after


lst = ["a", "b", "c", "a", "d", "c", "e"]
list(split_after(lst, lambda x: x == "c"))
# [['a', 'b', 'c'], ['a', 'd', 'c'], ['e']]

Another example, here we split words by simply changing the predicate:

lst = ["ant", "bat", "cat", "asp", "dog", "carp", "eel"]
list(split_after(lst, lambda x: x.startswith("c")))
# [['ant', 'bat', 'cat'], ['asp', 'dog', 'carp'], ['eel']]

+ A third-party library that implements itertools recipes and more. > pip install more_itertools

Upvotes: 6

Paul Rooney
Paul Rooney

Reputation: 21609

What about this. It should only iterate over the input once and some of that is in the index method, which is executed as native code.

def splitkeep(v, c):

    curr = 0
    try:
        nex = v.index(c)
        while True:
            yield v[curr: (nex + 1)]
            curr = nex + 1
            nex += v[curr:].index(c) + 1

    except ValueError:
        if v[curr:]: yield v[curr:]

print(list(splitkeep( ['a', 'b', 'c', 'a', 'd', 'c', 'e'], 'c')))

result

[['a', 'b', 'c'], ['a', 'd', 'c'], ['e']]

I wasn't sure if you wanted to keep an empty list at the end of the result if the final value was the value you were splitting on. I made an assumption you wouldn't, so I put a condition in excluding the final value if it's empty.

This has the result that the input [] results in only [] when arguably it might result in [[]].

Upvotes: 1

j4nw
j4nw

Reputation: 2405

stuff = ['a', 'b', 'c', 'a', 'd', 'c', 'e']

You can find out the indices with 'c' like this, and add 1 because you'll be splitting after it, not at its index:

indices = [i + 1 for i, x in enumerate(stuff) if x == 'c']

Then extract slices like this:

split_stuff = [stuff[i:j] for i, j in zip([0] + indices, indices + [None])]

The zip gives you a list of tuples analogous to (indices[i], indices[i + 1]), with the concatenated [0] allowing you to extract the first part and [None] extracting the last slice (stuff[i:])

Upvotes: 6

Ajay2588
Ajay2588

Reputation: 567

You can try using below snippet. Use more_itertools

>>> l = ['a', 'b', 'c', 'a', 'd', 'c', 'e']
>>> from more_itertools import sliced
>>> list(sliced(l,l.index('c')+1))

Output is:

[['a', 'b', 'c'], ['a', 'd', 'c'], ['e']]

Upvotes: 0

YuryChu
YuryChu

Reputation: 301

list_of_strings = ['a', 'b', 'c', 'a', 'd', 'c', 'e']

value = 'c'
new_list = []
temp_list = []
for item in list_of_strings:
    if item is value:
        temp_list.append(item)
        new_list.append(temp_list[:])
        temp_list.clear()
    else:
        temp_list.append(item)

if (temp_list):
    new_list.append(temp_list)

print(new_list)

Upvotes: 0

Artem Kryvonis
Artem Kryvonis

Reputation: 128

def spliter(value, array):
    res = []
    while value in array:
        index = array.index(value)
        res.append(array[:index + 1])
        array = array[index + 1:]
    if array:
        # Append last elements
        res.append(array)
    return res

a = ['a', 'b', 'c', 'a', 'd', 'c', 'e']
print(spliter('b',a))
# [['a', 'b'], ['c', 'a', 'd', 'c', 'e']]
print(spliter('c',a))
# [['a', 'b', 'c'], ['a', 'd', 'c'], ['e']]

Upvotes: 1

Ma0
Ma0

Reputation: 15204

How about this rather playful script:

a = ['a', 'b', 'c', 'a', 'd', 'c', 'e']

b = ''.join(a).split('c')  # ['ab', 'ad', 'e']

c = [x + 'c' if i < len(b)-1 else x for i, x in enumerate(b)]  # ['abc', 'adc', 'e']

d = [list(x) for x in c if x]
print(d)  # [['a', 'b', 'c'], ['a', 'd', 'c'], ['e']]

It can also handle beginnings and endings with a "c"

a = ['c', 'a', 'b', 'c', 'a', 'd', 'c', 'e', 'c']
d -> [['c'], ['a', 'b', 'c'], ['a', 'd', 'c'], ['e', 'c']]

Upvotes: 0

asongtoruin
asongtoruin

Reputation: 10359

You could try something like the following:

list_of_strings = ['a', 'b', 'c', 'a', 'd', 'c', 'e']

output = [[]]

for x in list_of_strings:
    output[-1].append(x)
    if x == 'c':
        output.append([])

Though it should be noted that this will append an empty list to your output if your input's last element is 'c'

Upvotes: 3

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