How to add a new column to a CSV file

Question

I have several CSV files that look like this   Input Name        Code blackberry  1 wineberry   2 rasberry    1 blueberry   1 mulberry    2   I would like to add a new column to all CSV files so that it would look like this   Output Name        Code    Berry blackberry  1   blackberry wineberry   2   wineberry rasberry    1   rasberry blueberry   1   blueberry mulberry    2   mulberry   The script I have so far is this   import csv with open input csv  r   as csvinput      with open output csv   w   as csvoutput          writer   csv writer csvoutput          for row in csv reader csvinput               writer writerow row   Berry       Python 3 2   But in the output  the script skips every line and the new column has only Berry in it   Output Name        Code    Berry blackberry  1   Berry  wineberry   2   Berry  rasberry    1   Berry  blueberry   1   Berry  mulberry    2   Berry

User · Answer

I don t see where you re adding the new column  but try this       import csv     i   0     Berry   open  newcolumn csv   r   readlines       with open input csv  r   as csvinput          with open output csv   w   as csvoutput              writer   csv writer csvoutput              for row in csv reader csvinput                   writer writerow row     Berry i                   i

User · Answer

Yes Its a old question but it might help some  import csv import uuid    read and write csv files with open  in file   r   as r csvfile      with open  out file   w  newline     as w csvfile           dict reader   csv DictReader r csvfile delimiter               add new column with existing         fieldnames   dict reader fieldnames     ADDITIONAL COLUMN           writer csv   csv DictWriter w csvfile fieldnames delimiter              writer csv writeheader             for row in dict reader              row  ADDITIONAL COLUMN     str uuid uuid4   int  gt  gt  64   0 6              writer csv writerow row

User · Answer

This code will suffice your request and I have tested on the sample code    import csv  with open in path   r   as f in  open out path   w   as f out      csv reader   csv reader f in  delimiter          writer   csv writer f out       for row in csv reader      writer writerow row    row 0

User · Answer

This should give you an idea of what to do    gt  gt  gt  v   open  C  test test csv    gt  gt  gt  r   csv reader v   gt  gt  gt  row0   r next    gt  gt  gt  row0 append  berry    gt  gt  gt  print row0   Name    Code    berry    gt  gt  gt  for item in r          item append item 0           print item            blackberry    1    blackberry     wineberry    2    wineberry     rasberry    1    rasberry     blueberry    1    blueberry     mulberry    2    mulberry    gt  gt  gt     Edit  note in py3k you must use next r   Thanks for accepting the answer  Here you have a bonus  your working script    import csv  with open  C  test test csv   r   as csvinput      with open  C  test output csv    w   as csvoutput          writer   csv writer csvoutput  lineterminator   n           reader   csv reader csvinput           all              row   next reader          row append  Berry           all append row           for row in reader              row append row 0               all append row           writer writerows all    Please note    the lineterminator parameter in csv writer  By default it is set to   r n  and this is why you have double spacing  the use of a list to append all the lines and to write them in one shot with writerows  If your file is very  very big this probably is not a good idea  RAM  but for normal files I think it is faster because there is less I O  As indicated in the comments to this post  note that instead of nesting the two with statements  you can do it in the same line   with open  C  test test csv   r   as csvinput  open  C  test output csv    w   as csvoutput

User · Answer

I used pandas and it worked well    While I was using it  I had to open a file and add some random columns to it and then save back to same file only   This code adds multiple column entries  you may edit as much you need   import pandas as pd  csv input   pd read csv  testcase csv            reading my csv file csv input  Phone1     csv input  Name            this would also copy the cell value  csv input  Phone2     csv input  Name   csv input  Phone3     csv input  Name   csv input  Phone4     csv input  Name   csv input  Phone5     csv input  Name   csv input  Country     csv input  Name   csv input  Website     csv input  Name   csv input to csv  testcase csv   index False     this writes back to your file   If you want that cell value doesn t gets copy  so first of all create a empty Column in your csv file manually  like you named it as Hours then   Now for this you can add this line in above code   csv input  New Value     csv input  Hours     or simply we can  without adding the manual column  we can  csv input  New Value            simple and easy   I Hope it helps

User · Answer

In case of a large file you can use pandas read csv with the chunksize argument which allows to read the dataset per chunk  import pandas as pd  INPUT CSV    quot input csv quot  OUTPUT CSV    quot output csv quot  CHUNKSIZE   1 000   Maximum number of rows in memory  header   True mode    quot w quot  for chunk df in pd read csv INPUT CSV  chunksize CHUNKSIZE       chunk df  quot Berry quot     chunk df  quot Name quot         You apply any other transformation to the chunk               chunk df to csv OUTPUT CSV  header header  mode mode      header   False   Do not save the header for the other chunks     mode    quot a quot     a  stands for append mode  all the other chunks will be appended  If you want to update the file inplace  you can use a temporary file and erase it at the end import pandas as pd  INPUT CSV    quot input csv quot  TMP CSV    quot tmp csv quot  CHUNKSIZE   1 000   Maximum number of rows in memory  header   True mode    quot w quot  for chunk df in pd read csv INPUT CSV  chunksize CHUNKSIZE       chunk df  quot Berry quot     chunk df  quot Name quot         You apply any other transformation to the chunk               chunk df to csv TMP CSV  header header  mode mode      header   False   Do not save the header for the other chunks     mode    quot a quot     a  stands for append mode  all the other chunks will be appended  os replace TMP CSV  INPUT CSV

User · Answer

import csv with open  input csv   r   as csvinput      with open  output csv    w   as csvoutput          writer   csv writer csvoutput           for row in csv reader csvinput               if row 0      Name                   writer writerow row   Berry                else                  writer writerow row  row 0      Maybe something like that is what you intended   Also  csv stands for comma separated values   So  you kind of need commas to separate your values like this I think   Name Code blackberry 1 wineberry 2 rasberry 1 blueberry 1 mulberry 2

User · Answer

Append new column in existing csv file using python without header name   default text    Some Text    Open the input file in read mode and output file in write mode     with open  problem-one-answer csv    r   as read obj        open  output 1 csv    w   newline     as write obj    Create a csv reader object from the input file object     csv reader   reader read obj    Create a csv writer object from the output file object     csv writer   csv writer write obj    Read each row of the input csv file as list     for row in csv reader    Append the default text in the row   list         row append default text    Add the updated row   list to the output file         csv writer writerow row   Thankyou

User · Answer

For adding a new column to an existing CSV file with headers   if the column to be added has small enough number of values  here is a convenient function  somewhat similar to  joaquin s solution   The function takes the  Existing CSV filename Output CSV filename  which will have the updated content  and List with header name amp column values  def add col to csv csvfile fileout new list       with open csvfile   r   as read f            open fileout   w   newline     as write f          csv reader   csv reader read f          csv writer   csv writer write f          i   0         for row in csv reader              row append new list i               csv writer writerow row              i    1   Example  new list1     test hdr  4 4 5 5 9 9 9  add col to csv  exists csv   new-output csv  new list1   Existing CSV file   Output updated  CSV file

User · Answer

I m surprised no one suggested Pandas  Although using a set of dependencies like Pandas might seem more heavy-handed than is necessary for such an easy task  it produces a very short script and Pandas is a great library for doing all sorts of CSV  and really all data types  data manipulation  Can t argue with 4 lines of code   import pandas as pd csv input   pd read csv  input csv   csv input  Berries     csv input  Name   csv input to csv  output csv   index False    Check out Pandas Website for more information   Contents of output csv   Name Code Berries blackberry 1 blackberry wineberry 2 wineberry rasberry 1 rasberry blueberry 1 blueberry mulberry 2 mulberry

[python] How to add a new column to a CSV file?

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