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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.

``````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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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

The actual performance issue
Alexei‭ wrote 2 months ago:

Can you provide the actual waiting time for running your code? Example: run your code for 10K times and tell us how much it took to end.

sfrow‭ wrote 2 months ago:

Actually you are right. For 10k rows it's taking 14 seconds, which is not so bad. For the whole list of 300k it will take 7-8 minutes.

elgonzo‭ wrote 2 months ago:

If 14 sec for 10k rows "is not so bad", then 7 min for 300k rows is not worse and not so bad either. Because, given 7 min for 300k rows, each of the thirty 10k rows in those 300k rows still take around 14 sec.

sfrow‭ wrote 2 months ago:

First time when I run it took me almost 1 hour, but I found that the file contain several wrong data in the column and this cause the problem for the long run.

hkotsubo‭ wrote 2 months ago:

sfrow‭ I've made this test and surprisingly using string slices is faster than doing the math. Try to change the algorithm and see if it makes some difference

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