Question

Say I have two lists

[16, 0, 0, ';', 17, 0, 2, ';', 0, 2, 1, ';']
  [-1, 0, ';', 0, -2, ';', -2, -1, ';']

Is there a simpler way to merge these list elements conditionally on meeting the ‘;’ character than individually iterating through them both and combining them?

The output should be

[16, 0, 0, -1, 0, ';', 17, 0, 2, 0, -2, ';', 0, 2, 1, -2, -2,';']

Answer 1

def get_part(lst,sep=';'):
    out = []
    for i in lst:
        if i == sep:
           yield out
           out = []
        else:
           out.append(i)

Now we can zip together your lists:

merged = []
for l1,l2 in zip(get_part(list1),get_part(list2)):
    merged.extend(l1)
    merged.extend(l2)
    merged.append(';')

Of course, at it’s core, this is essentially iterating over both of them and combining … so in answer to your question, I don’t think there’s a better way.

---

Perhaps a better way to store your lists would be storing them as a list of lists — e.g.:

list1 = [[16, 0, 0], [ 17, 0, 2], [ 0, 2, 1] ]

stored like this, you can just do:

merged = [ l1 + l2 for l1,l2 in zip(list1,list2) ]