CODEWITHSUNDEEP
pythonlistpython-3.x
Jia Li
Jia Li

Reputation: 5

python compare two lists and replace original list if there is a match

I have two lists containing strings. I want to take each item in the base_list and search to see if there is a match for the first 3 characters in any values from the custom list. If there is a match, replace the original value in base_list with the one from custom_list. If there is no match, keep the original value.

base_list = ["abc123", "cde123", "efg456", "ghi123"]

custom_list = ["abc321", "efg654"]

Desired Output:

modified_base_list = ["abc321", "cde123", "efg654", "ghi123"]

Eventually I also want to write this new modified_base_list as a file containing the items, one per line.

I've tried:

modified_base_list = []

for custom in custom_list:
    for base in base_list:
        if custom[:3] == base[:3]:
            modified_base_list.append(custom)
        else:
            modified_base_list.append(base)


print(modified_base_list)

with open('newfile.txt', 'w') as f:
    for s in modified_base_list:
        f.write(s)

***EDITING QUESTION to account for lists that have 15k+ lines to find a faster way to do this.

Upvotes: 0

Views: 2576

Answers (4)

Abdou
Abdou

Reputation: 13274

You can use a combination of list comprehension and map for this:

base_list = ["abc123", "cde123", "efg456", "ghi123"]

custom_list = ["abc321", "efg654"]

smaller_custom = [y[:3] for y in custom_list]

modified_base_list = ["**{}**".format(custom_list[smaller_custom.index(x[:3])]) if x[:3] in smaller_custom else x for x in base_list]
# ['**abc321**', 'cde123', '**efg654**', 'ghi123']

with open('output_data.txt','w') as outfile:
    outfile.write("\n".join(modified_base_list))

I hope this helps.

Upvotes: 0

ettanany
ettanany

Reputation: 19806

Try the following with filter():

res = []

for i in base_list:
    temp = list(filter(lambda j: j[:3] == i[:3], custom_list))
    if temp:
        res.append('**{}**'.format(temp.pop()))
    else:
        res.append(i)

Output:

>>> res
['**abc321**', 'cde123', '**efg654**', 'ghi123']

Upvotes: 0

poke
poke

Reputation: 387557

This is a solution that mutates the original list, replacing only those where the desired match exists:

>>> base_list = ["abc123", "cde123", "efg456", "ghi123"]
>>> custom_list = ["abc321", "efg654"]
>>> for i, x in enumerate(base_list):
        for test in custom_list:
            if test[:3] == x[:3]:
                base_list[i] = test
                break

>>> base_list
['abc321', 'cde123', 'efg654', 'ghi123']

Of course if you don’t want to modify the original list, you can create a coopy of it first using modified_base_list = base_list[:].

You can also follow your own idea but in that case, you have to make sure that you are primarily iterating over base_list and won’t add items multiple times:

modified_base_list = []
for base in base_list:
    found = False
    for custom in custom_list:
        if custom[:3] == base[:3]:
            modified_base_list.append(custom)
            found = True
            break

    if not found:
        modified_base_list.append(base)

You can also use for…else here instead of that utility variable found:

for base in base_list:
    for custom in custom_list:
        if custom[:3] == base[:3]:
            modified_base_list.append(custom)
            break
    else:
        modified_base_list.append(base)

Upvotes: 1

Chris_Rands
Chris_Rands

Reputation: 41168

You could use a list comprehension containing a generator expression:

base_list = ["abc123", "cde123", "efg456", "ghi123"]
custom_list = ["abc321", "efg654"] 
modified_base_list = [next((y for y in custom_list if y[:3] == x[:3]), x) for x in base_list]
# ['abc321', 'cde123', 'efg654', 'ghi123']

Note that I'm assuming if the same 3 character prefix occurs multiple times in custom_list that you only wish to take the first instance.

Upvotes: 0

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