Splitting a list based on specific element

Question

I am trying to split my list into sublists based on the condition that anything within the element '|' would be considered as the elements for a new sublist. I am ignoring any elements with empty strings so those wont be included in the final list. I have the following list:

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

The resulting result would then be:

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

I have written the following code, can someone show me how to solve this please:

start = 0; end = 0
nlist = []
for s in range(0, len(slist)-1):
    ns = s + 1
    if slist[s] == '|' and  ns == '|':
        end = s - 1
    elif slist[s] == '|':
        start = s + 1
        nlist.append(nlist[start:end])

`[list(l) for l in "".join(slist).split("|") if l]` you did not ask a question so I assume you just want a solution — Nearoo, May 15 '22 at 12:15
@Nearoo This solution assumes that you only have characters in the list. If any element is a string you get a different result than expected... — simre, May 15 '22 at 12:17
I am ignoring any elements with empty strings so those wont be included in the final list — Kaarthik, May 15 '22 at 12:21
Based on the stated rules the output should be [['a', 'b', 'c'], [''], ['d', 'e']] — DarkKnight, May 15 '22 at 12:21
What would happen if either the first or last elements were not '|' ? — DarkKnight, May 15 '22 at 12:22
@LancelotduLac edited the question. I am ignoring any elements with empty strings. — Kaarthik, May 15 '22 at 12:23

score 1 · Answer 1 · answered May 15 '22 at 12:27

One possible solution:

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

inList = False
res = []
subl = []
for e in slist:
    if not inList and e == '|':
        # Only to find the start.
        inList = True
    elif inList:
        if e == '|':
            if len(subl) > 0:
                # Append only if subl is not empty
                res.append(subl)
            subl = []
        elif e:
            # Append only non empty elements
            subl.append(e)

res:

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

score 1 · Answer 2 · answered May 15 '22 at 12:28

Unless you really need the indices for something, in Python you should rather loop over the elements directly. Then it's just a couple if-s, to decide what to do with the current element:

slist = ['|', 'a', 'b', 'c', '|', '', '|', 'd', 'e', '|']
nlist = [[]]
for x in slist:
  if x != "":               # ignore empty
    if x == "|":
      nlist.append([])      # add a new sub-list
    else:
      nlist[-1].append(x)   # or append the element to the current one

At this point nlist has empty sub-lists:

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

Which you can filter out with a simple list comprehenstion:

[l for l in nlist if len(l) != 0]

Outputs

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

score 1 · Accepted Answer · answered May 15 '22 at 12:31

The split/join technique advocated by @simre works for the data shown in the question. Here's a loop-based approach that may be more flexible:

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

result = []
e = []

for v in slist:
    if v == '|':
        if e:
            result.append(e)
            e = []
    elif v:
        e.append(v)

print(result)

Output:

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

This also works where the strings in the list are comprised of more than one character. There is an implicit reliance on the last element in the list being equal to '|'.

DontDownvote · Answer 4 · 2022-05-15T12:37:20.153

0

slist = ['|', 'a', 'b', 'c', '|', '', '|', 'd', 'e', '|']
relevant =[ i for i , x in enumerate(slist) if x =='|']
i=0
new=[[]]
while(len(slist)>0 and i!=len(relevant)):
    x=slist[relevant[i]+1:relevant[i+1]]
    new[0].append(x)
    i=i+2
print(new)

Another way

edited May 15 '22 at 12:37

answered May 15 '22 at 12:36

DontDownvote

182
7

Splitting a list based on specific element

4 Answers4