CODEWITHSUNDEEP
python-3.x
SEG
SEG

Reputation: 1

how to concatenate two lists of different lengths to fill in missing values

I am trying to add elements from one list to another list that has part of the elements but some are missing

days_m = ['1','2','3']
dates = ['4-','10-','10-20','10-4','9-']
start_end = []

for f,b in itertools.zip_longest(dates, days_m, fillvalue = 'NA'):
    if len(f) < 4:
        date = f+b
        start_end.append(date)
    elif len(f) >= 4:
        start_end.append(date)

I expect the output to be 

['4-1', '10-2', '10-20', '10-4', '9-3']

But the actual output has been 

['4-1', '10-2', '10-2', '10-2', '9-NA']

Upvotes: 0

Views: 97

Answers (1)

Jean-Fran&#231;ois Fabre
Jean-Fran&#231;ois Fabre

Reputation: 140196

First, you cannot use zip_longest here. Because you mean to pick a value from the second list only if the length is < 4. zip_longest does that all the time.

Then, you're not updating date in the second branch.

I suggest to use iter on days_m, and iterate on it manually with next, with the default value of "NA". Also drop the double length test as it is redundant.

And always use an updated version of f. Just concatenate to it when needed, else use as-is.

days_m = iter(['1','2','3'])
dates = ['4-','10-','10-20','10-4','9-']
start_end = []

for f in dates:
    if len(f) < 4:
        f += next(days_m,"NA")
    start_end.append(f)

print(start_end)

result:

['4-1', '10-2', '10-20', '10-4', '9-3']

Upvotes: 1

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