concatenating Columns within a dataframe

Question

I have a large csv file where I have filtered out the rows I want and created smaller more manageable data frames (called 'CL'). Each row has a Contract Month and Contract Year both in Int64 (I believe). I want to create a column combining the two in a date format (e.g., MM-YYYY) and having difficulty.

I have tried both extracting the columns to pandas series and converting to string

series.to_string

as well as the individual columns with

CL['CONTRACT MONTH']= CL['CONTRACT MONTH'].astype(str)

The latter method gives me a message "... SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead"

A little over my head with this (just learning Python) and was hoping for some help.

Would you want to store the combined date as an integer?

ALollz
– ALollz

2018-07-02 17:20:21 +00:00
Commented Jul 2, 2018 at 17:20 — ALollz
– ALollz, Commented Jul 2, 2018 at 17:20

jpp · Accepted Answer · 2018-07-02 16:55:13Z

3

You can concatenate strings within Pandas series using +. In addition, you can use pd.Series.str.zfill to ensure months always have 2 characters:

df = pd.DataFrame([[10, 1995], [3, 1996], [2, 1998], [5, 2000]],
                  columns=['MONTH', 'YEAR'])

df['DATE'] = df['MONTH'].astype(str).str.zfill(2) + '-' + df['YEAR'].astype(str)

print(df)

   MONTH  YEAR     DATE
0     10  1995  10-1995
1      3  1996  03-1996
2      2  1998  02-1998
3      5  2000  05-2000

Your SettingWithCopyWarning may not represent a problem per se. It is often a guess by Pandas that you are operating on a copy rather than a view. You may safely ignore this warning if you see it with the above solution.

answered Jul 2, 2018 at 16:55

jpp

166k37 gold badges301 silver badges363 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Chris L Over a year ago

one little snag...if I would want the new 'Date' to be come the index how would I do it? I tried df.set_index(df['DATE']) but doesn't work.

jpp Over a year ago

@ChrisL, Reassign back to df, i.e. df = df.set_index(df['DATE'])

Collectives™ on Stack Overflow

concatenating Columns within a dataframe

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related