map US state name to two letter acronyms that was given in dictionary separately

Question

Suppose now I have a dataframe with 2 columns: State and City.

Then I have a separate dict with the two-letter acronym for each state. Now I want to add a third column to map state name with its two-letter acronym. What should I do in Python/Pandas? For instance the sample question is as follows:

import pandas as pd
a = pd.Series({'State': 'Ohio', 'City':'Cleveland'})
b = pd.Series({'State':'Illinois', 'City':'Chicago'})
c = pd.Series({'State':'Illinois', 'City':'Naperville'})
d = pd.Series({'State': 'Ohio', 'City':'Columbus'})
e = pd.Series({'State': 'Texas', 'City': 'Houston'})
f = pd.Series({'State': 'California', 'City': 'Los Angeles'})
g = pd.Series({'State': 'California', 'City': 'San Diego'})
state_city = pd.DataFrame([a,b,c,d,e,f,g])
state_2 = {'OH': 'Ohio','IL': 'Illinois','CA': 'California','TX': 'Texas'}

Now I have to map the column State in the df state_city using the dictionary of state_2 . The mapped df state_city should contain three columns: state , city , and state_2letter .

The original dataset I had had multiple columns with nearly all US major cities.

Therefore it will be less efficient to do it manually. Is there any easy way to do it?

Answer 1

For one, it's probably easier to store the key-value pairs like state name: abbreviation in your dictionary, like this:

state_2 = {'Ohio': 'OH', 'Illinois': 'IL', 'California': 'CA', 'Texas': 'TX'}

You can achieve this easily:

state_2 = {state: abbrev for abbrev, state in state_2.items()}

Using pandas.DataFrame.map :

>>> state_city['abbrev'] = state_city['State'].map(state_2)
>>> state_city
          City       State abbrev
0    Cleveland        Ohio     OH
1      Chicago    Illinois     IL
2   Naperville    Illinois     IL
3     Columbus        Ohio     OH
4      Houston       Texas     TX
5  Los Angeles  California     CA
6    San Diego  California     CA

Answer 2

I do agree with @blacksite that the state_2 dictionary should map its values like that:

state_2 = {'Ohio': 'OH','Illinois': 'IL','California': 'CA','Texas': 'TX'}

Then using pandas.DataFrame.replace

state_city['state_2letter'] = state_city.State.replace(state_2)
state_city

|-|State      |City         |state_2letter|
|-|-----      |------       |----------|
|0| Ohio      | Cleveland   |   OH|
|1| Illinois  | Chicago     |   IL|
|2| Illinois  | Naperville  |   IL|
|3| Ohio      | Columbus    |   OH|
|4| Texas     | Houston     |   TX|
|5| California| Los Angeles |   CA|
|6| California| San Diego   |   CA|