How would I check if a list is in another list in the same order?

Question

Basically for an assignment I need to determine if a list is a sublist of another list, which I saw was answered in this post Checking if list is a sublist, however there are some special requirements, that will be explained in the examples, that werent answered in that post. I also saw this post How to check if a list is in another list with the same order python which also didnt help determine the special requirements.

Example1:

list1 = 'a,q,b,q,q,q,q,q,q,c'
sublist = 'a,b,c'
output -> True

Explanation: Now, I know this isn't necessarily a sublist of list1, but a, b, and c are all present in list1, in the same order as the sublist variable, with only q separating them, which I can ignore because q isnt in sublist, which is why this would output true.

Example2:

list1 = 'b,q,q,q,q,a,q,c'
sublist = 'a,b,c'
output -> False

Explanation: Although this list does contain a, b, and c like the other example, it is out of order, hence why it would be false

Example3:

list1 = 'a,b,b,q,c'
sublist = 'a,b,c'
output -> False

Example4:

list1 = 'a,b,b,a,b,q,c'
sublist = 'a,b,c'
output -> True

Explanation: At the beginning of the list we have a,b,b which in the before explanation I stated was false, however following that part we have the correct order of a,b,c with a q separating the b and c

Here is my code. The problem I can't seem to find shows up in one hidden test case I have to run this through, I cant see the input or the output, which is making it hard to debug this. I've tried to run many of my own different test cases, but I can't seem to find what I'm missing here. I'm just wondering if anyone can figure out what I'm forgetting to take into account when running this.

sublist = 'a,b,c'.split(',')
l1 = 'a,q,b,a,q,q,q,q,q,q,q,q,q,c'.split(',')
item_order = []

for item in l1:
    #Check if I have found a sublist
    if item_order == sublist:
        break

    #If item is in sublist, but hasnt been seen yet
    elif item in sublist and item not in item_order:
        item_order.append(item)
        print('adding item', item_order)

    #If item has been seen and is in sublist
    elif item in item_order:
        #Reset and add duplicated item 
        item_order = []
        item_order.append(item)
        print('found duplicate, resetting list', item_order)

if item_order == sublist: print("true")
else: print("false")

It might of been confusing. Sorry if it is. I spent awhile trying to make it as clear as I can. — Arxci, Feb 25 '20 at 01:56
Your code has a check for repeated items, but the description doesn't say how they're supposed to be handled. Neither of the examples demonstrates it. — Barmar, Feb 25 '20 at 01:58
Ok, so a,b,b,q,c will not be a match to a,b,c because the sublist a,b,c has only one b, while the list a,b,b,q,c has two. Which I why I have to do the check for duplicates — Arxci, Feb 25 '20 at 02:04
So the gist of your question is: "There's something wrong with my code, but I don't know what it is. Please help me fix it." — martineau, Feb 25 '20 at 02:06

Pedro Lobito · Accepted Answer · 2020-02-25T15:52:13.090

3

You can filter the elements from list1 that doesn't exist in sublist and compare it with sublist, i.e.:

def good_seq(list1, sublist):
    return [x for x in list1.split(",") if x in sublist.split(",")] == sublist.split(",")

Demo

edited Feb 25 '20 at 15:52

answered Feb 25 '20 at 01:49

Pedro Lobito

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score 1 · Answer 2 · answered Feb 25 '20 at 02:02

Can you try the following:

def dedupe(items):
    """Function to remove duplicate by preserving its order

    Args:
        items (list): the list  for which the duplicates must be removed

    Yields:
        generator: the generator with unique items
    """
    seen = set()
    for item in items:
        if item not in seen:
            yield item
            seen.add(item)

def check_order(l1, sublist):
    l1 = list(dedupe(l1))
    result = [val for val in l1 if val in sublist] == sublist
    return result

sublist = 'a,b,c'.split(',')
l1 = 'a,q,b,a,q,q,q,q,q,q,q,q,q,c'.split(',')
print(check_order(l1, sublist))

sublist = 'a,b,c'.split(',')
l1 = 'b,q,q,q,q,a,q,c'.split(',')
print(check_order(l1, sublist))

Output:

True
False

How would I check if a list is in another list in the same order?

2 Answers2