Q: [Pandas] How to efficiently assign unique ID to individuals with multiple entries based on name in very large df

Question

I\'d like to take a dataset with a bunch of different unique individuals, each with multiple entries, and assign each individual a unique id for all of their entries. Here\'

Answer 1

This method allow the 'id' column name to be defined with a variable. Plus I find it a little easier to read compared to the assign or groupby methods.

# Create Dataframe
df = pd.DataFrame(
    {'FirstName': ['Tom','Tom','David','Alex','Alex'],
    'LastName': ['Jones','Jones','Smith','Thompson','Thompson'],
    })

newIdName = 'id'   # Set new name here.

df[newIdName] = (df['LastName'] + '_' + df['FirstName']).astype('category').cat.codes     

Output:

>>> df
          FirstName  LastName  id
        0       Tom     Jones   0
        1       Tom     Jones   0
        2     David     Smith   1
        3      Alex  Thompson   2
        4      Alex  Thompson   2