Remove next elements from list in python

Question

I have a list like the following:

['ABC ', '02:20', 123456, 123, '-', 123456, 123, 'DEF ', '-', 123456, 123, '-', 123456, 123, 'IFG', '-', 123456, 123, '-', 123456, 123, 'IJK', '03:40', 123456, 123, '-', 123456, 123, 'LOM', '-', 123456, 123, '03:00', 123456, 123]

How do I delete next two elements along with current element based on a condition ?

Such as I want to delete - and the next 2 elements as well

for idx, val in enumerate(n1):
    if val == '-':
        del n1[idx]
        del n1[idx+1]
        del n1[idx+2]
        n1 = n1
        

But only - is removed from the list

Answer 1

1. First problem is that after executing del n1[idx] , the next value, previously at idx+1 is now at position idx as it have moved forward, so to delete 3 consecutives elements the code would

   del n1[idx] del n1[idx] del n1[idx] # OR del n1[idx:idx+3]

2. But as you iterating while removing, you'll miss elements, and you code would return the following, there 5 removals done but 2 misses

   ['ABC ', '02:20', 123456, 123, 'DEF ', '-', 123456, 123, 'IFG', '-', 123456, 123, 'IJK', '03:40', 123456, 123, 'LOM', '03:00', 123456, 123]

---

A solution is to not iterate, but rather check&remove until there is no '-' left

while '-' in n1:
    idx = n1.index('-')
    del n1[idx:idx + 3]

Answer 2

您可以通过以下方式从列表中删除元素，

del n1[idx:idx+2]

Answer 3

Each time you execute del n1[idx] , an element will be removed from the list, and therefore the indices of all elements after the deleted one will change.

Therefore, the following del n1[idx+1] will be deleting the wrong element.

To avoid this, you can delete the elements in decreasing order of index:

del n1[idx+2]
del n1[idx+1]
del n1[idx]

(And of course you should check if idx+2 and idx+1 are still within the bounds of the list).

Answer 4

just loop and create a new list based on your logic. see below

lst = ['ABC ', '02:20', 123456, 123, '-', 123456, 123, 'DEF ', '-', 123456, 123, '-', 123456, 123, 'IFG', '-', 123456,
       123, '-', 123456, 123, 'IJK', '03:40', 123456, 123, '-', 123456, 123, 'LOM', '-', 123456, 123, '03:00', 123456,
       123]
idx = 0
lst1 = []
while idx < len(lst) - 1:
    if lst[idx] == '-':
        idx += 3
    else:
        lst1.append(lst[idx])
        idx += 1
print(lst1)

output

['ABC ', '02:20', 123456, 123, 'DEF ', 'IFG', 'IJK', '03:40', 123456, 123, 'LOM', '03:00', 123456]

Answer 5

Not elegant but works and easily understandable, can easily be used with numba if the dataset is huge.

n1 = ['ABC ', '02:20', 123456, 123, '-', 123456, 123, 'DEF ', '-', 123456, 123, '-', 123456, 123, 'IFG', '-', 123456, 123, '-', 123456, 123, 'IJK', '03:40', 123456, 123, '-', 123456, 123, 'LOM', '-', 123456, 123, '03:00', 123456, 123]

skip = 0
result = []
for idx, val in enumerate(n1):
    if val == '-':
        skip = 3
    else:
        skip -= 1
        if skip <= 0:
            result.append(val)