I've found similar but not identical questions 742371 and 4081217 with great answers, but haven't come to a solution to my problem.
I'm trying to process items in a list in place while it's being looped over, and re-loop over what's remaining in the list if it has not met a conditional. The conditional will eventually be met as True for all items in the list, but not necessarily on a "known" iteration. It reminds me of building a tree to some degree, as certain items in the list must be processed before others, but the others may be looped over beforehand.
My first instinct is to create a recursive function and edit a slice copy of the list. However I'm having little luck ~
I won't initially know how many passes it will take, but it can never be more passes than elements in the list... just by the n开发者_开发问答ature of at least one element will always meet the conditional as True
Ideally ... the result would be something like the following
# initial list
myList = ['it1', 'test', 'blah', 10]
newList = []
# first pass
newList = ['test']
# 2nd pass
newList = ['test', 'blah', 10]
# 3rd pass
newList = ['test', 'blah', 10, 'it1']
current = ['it1', 'test', 'blah', 10]
results = []
while current:
remaining = []
for item in current:
(results if meets_conditional(item) else remaining).append(item)
current = remaining
How about something like this (just made up a silly condition so I could test it):
import random
myList = ['it1', 'test', 'blah', 10]
newList = []
def someCondition(var):
return random.randrange(0,2) == 0
def test():
while len(myList) > 0:
pos = 0
while pos < len(myList):
if someCondition(myList[pos]): # with someCondition being a function here
newList.append(myList.pop(pos))
else:
pos += 1
if __name__ == '__main__':
test()
print(myList)
print(newList)
[Result:]
[]
['it1', 10, 'blah', 'test']
A brute force approach would be to create a temporary list of booleans the same size as your original list initialized to False
everywhere.
In each pass, whenever the item at index i
of the original list meets the condition, update the value in the temporary array at index i
with False.
In each subsequent pass, look only at the values where the corresponding index is False
. Stop when all values have become True
.
Grr, come to think of it, keep a set
of indexes that have met the condition. Yes, sets are better than arrays of booleans.
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