Python - Read CSV Columns Into List

18 Comments

1. how can we change column values from string to float in csv file in python?

   • The above example is to read values from a CSV file and after reading a value into list you can convert it using the float() function.

     If I am not getting it right, then describe you question in more detail on our forum orclqa.com

2. How to parse subcolumn in nested column?

   Example:
   import csv

   with open("country.csv", "r") as csv_file:
      csv_reader = csv.DictReader(csv_file, delimiter=',')
      for lines in csv_reader:
        print(lines['COUNTRY'], lines['CAPITAL'])

       AR Argentina Buenos Aires

   Country has data Country_ID and Country_Name.
   I want to remove first subcolumn Country_ID.

   How to achieve that?

   • I think you have to use the functions to pick the substring of a string. For example, if you know that the country id is of 2 character length, then you can use the slicing method as following:

     with open("country.csv", "r") as csv_file:
       csv_reader = csv.DictReader(csv_file, delimiter=’,’)
       for lines in csv_reader:
        c = lines[‘COUNTRY’]
        c = [3:]
     

     Now the first 3 characters (country id and a space) will be removed from lines['COUNTRY'].

   • Is there any method?
     because I don't know exactly the characters length of the first subcolumn.
     It's only has delimiter (for example white space or tab)

   • You can use split() function.

     Example:

     country = c.split(" ", 1)[1]
     

     it will split on a space and will limit to one split.

   • Great.
     can you help me how to trim and save it to output file?

   • You need to follow the below steps to write to a file using Python:

     file1 = open("myfile.txt","w") 
     Line = ["This is Delhi \n","This is Paris \n","This is London \n"]  
       
     file1.write("Hello \n") 
     file1.writelines(Line) 
     file1.close()
     

   • Ok. thank you very much

3. how to get it in same line?

   • Put end = " " in the end of print command. Following are the examples:

     print(lines[1], end =" ")
     

     or

     print(lines['COUNTRY_ID'], lines['COUNTRY_NAME'], end = " ")
     

     For Python version 2.x, add comma in end:

     print(lines[1]),
     

4. How to select a specific column value and use it in a iteration?

   • Check the below example:

     import csv
     
     with open("country.csv", "r") as csv_file:
       csv_reader = csv.DictReader(csv_file, delimiter=',')
       n = 0
       v_column_value = ""
       for lines in csv_reader:
        print(lines['COUNTRY_ID'], lines['COUNTRY_NAME'])
        if n == 0:
          v_column_value = lines(['COUNTRY_NAME'])
          n = 1
     

          
     The variable v_column_value will be assigned a country name value if the variable n is 0.

     And after assigning, it will set n to 1, so that in next iteration it will not change.

     So now you have the value of a column in a variable, you can use it in whole iteration.

   •   if n = 0:
          ^
     SyntaxError: invalid syntax

     still have the same problem, when I wrote my own code and when I pasted yours. do you have any idea why is that?

   • oh it was mistake in the code, it should be if n== 0: instead of if n=0:.

5. how to sum the paticular column in csv file

6. How to know how many lines on the csv file and how to print only for certain line, lets say print line 3
   Thank you

7. How would I add a column or multiple column to separate lists using this format

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