How to copy and paste dataframe rows into a web page textarea field
The better approach will be capture all the the data in a List, Later while pasting it you can check the length of the list, and later iterate through the list and paste the data 20 at a time in the text area. I hope this will solve your problem.
I have a dataframe with a single column "Cntr_Number" with x no of rows.
What i trying to achieve is using selenium to copy and paste the data into the web page textarea.
The constraint is that the web page text area only accept 20 rows of data per submission.
So how can i impplment it using while loop or other method.

Copy and paste the first 20 rows of data and click on the "Submit"
button 
Copy and paste the next 20 rows of data and click on the
"Submit" button

repeat the cycle until the last row.
Sorry i dont have any sample code to show but this is what I'm trying to achieve.
Appreciate if could have some sample code on how to do the implmentation.