Add new column in Pandas DataFrame Python

Question

I have dataframe in Pandas for example   Col1 Col2 A     1  B     2 C     3   Now if I would like to add one more column named Col3 and the value is based on Col2  In formula  if Col2   1  then Col3 is 0  otherwise would be 1  So  in the example above  The output would be   Col1 Col2 Col3 A    1    1 B    2    0 C    3    0   Any idea on how to achieve this

User · Accepted Answer

You just do an opposite comparison  if Col2  lt   1  This will return a boolean Series with False values for those greater than 1 and True values for the other  If you convert it to an int64 dtype  True becomes 1 and False become 0   df  Col3      df  Col2    lt   1  astype int    If you want a more general solution  where you can assign any number to Col3 depending on the value of Col2 you should do something like   df  Col3     df  Col2   map lambda x  42 if x  gt  1 else 55    Or   df  Col3     0 condition   df  Col2    gt  1 df loc condition   Col3     42 df loc  condition   Col3     55

User · Answer

The easiest way that I found for adding a column to a DataFrame was to use the  add  function   Here s a snippet of code  also with the output to a CSV file  Note that including the  columns  argument allows you to set the name of the column  which happens to be the same as the name of the np array that I used as the source of the data       now to create a PANDAS data frame df   pd DataFrame data   FF maxRSSBasal  columns   FF maxRSSBasal      from here on  we use the trick of creating a new dataframe and then  add ing it df2   pd DataFrame data   FF maxRSSPrism  columns   FF maxRSSPrism    df   df add  df2  fill value 0   df2   pd DataFrame data   FF maxRSSPyramidal  columns   FF maxRSSPyramidal    df   df add  df2  fill value 0   df2   pd DataFrame data   deltaFF strainE22  columns   deltaFF strainE22    df   df add  df2  fill value 0   df2   pd DataFrame data   scaled  columns   scaled    df   df add  df2  fill value 0   df2   pd DataFrame data   deltaFF orientation  columns   deltaFF orientation    df   df add  df2  fill value 0    print df  df to csv  FF data frame csv

[python] Add new column in Pandas DataFrame Python

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