How can I use a python dictionary to change the mapping of values within a pandas dataframe?-CodePudding

I am working with a pandas dataframe with just two columns market_mechanism and execution_venue.

e.g.

market_mechanism       execution_venue
      4                     AQXE
      5                     AQXE
      6                     AQEU
      5                     AQEU

When the market mechanism is 5, I would like to map AQXE -> ABCD and AQEU -> DCBA. Otherwise I would like to leave them as they are.

I want to use a dictionary to do this; I am close but can't quite get it. Here is my code:

trades_df.loc[trades_df['market_mechanism'] == '5',
                      'execution_venue'] = {'AQXE': 'AQXA', 'AQEU': 'AQEA'}.get(not_sure_what_goes_here)

I know the syntax for dictionary and doing a get in this case is perfect, but I'm not sure what to insert to refer to the input execution_venue.

CodePudding user response：

You could try this:

d = {'AQXE' : 'ABCD', 'AQEU' : 'DCBA'}

df['execution_venue'] = df['execution_venue'].mask(df['market_mechanism'].eq(5), df['execution_venue'].map(d))
df

   market_mechanism execution_venue
0                 4            AQXE
1                 5            ABCD
2                 6            AQEU
3                 5            DCBA

or else similar to your own approach:

df.loc[df['market_mechanism'].eq(5), 'execution_venue'] = df['execution_venue'].map(d)