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Python looping 300 000 rows

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Based on my last question comes new one.
How to loop over 300 000 rows and edit each row string one by one? I have a list of 11-digit numbers stored in one single column in Excel, and I need to separate the digits according to this pattern: 2-2-1-3-3.

I use the code below to loop to test the solution for only 20 rows and it's working.

Example: 00002451018 becomes 00 00 2 451 018.

priceListTest contains the column Column1 which has these 11 digit numbers. Somehow I need to loop all over these 300 000 rows and use the get_slices to change the pattern for each row like from the example above and store it into the new column New Value.

The for index, row it's working very slowly when I have to use it for 300 000 rows. Maybe there is a better method, but I'm new to python.

Thanks in advance!

for index, row in priceListTest.iterrows(): 
    #print(index,row)
    def get_slices(n, sizes, n_digits=11):
        for size in sizes:
            n_digits -= size
            
            val, n = divmod(n, 10 ** n_digits)
            yield f'{val:0{size}}'

    n = row['Column1']
    newVar = (' '.join(get_slices(n, [2, 2, 1, 3, 3])))
    priceListTest.at[index,['New Value']] = newVar
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5 comment threads

Parallel execution (1 comment)
The actual performance issue (5 comments)
Types (1 comment)
Create the function just once (3 comments)
A small note regarding MCVE (1 comment)

Comments on Python looping 300 000 rows

A small note regarding MCVE
FoggyFinder‭ wrote 2 months ago:

Disclaimer: I don't know enough about Python to suggest alternative approaches.

Anyway, when it comes to performance Qs I'd recommend providing full working MCVE since it's easily to overlook something. It might turn out that a culprit lays in a totally different area.