[pandas] pandas dataframe convert column type to string or categorical

Prior answers focused on nominal data (e.g. unordered). If there is a reason to impose order for an ordinal variable, then one would use:

# Transform to category
df['zipcode_category'] = df['zipcode_category'].astype('category')

# Add ordered category
df['zipcode_ordered'] = df['zipcode_category']

# Setup the ordering
df.zipcode_ordered.cat.set_categories(
    new_categories = [90211, 90210], ordered = True, inplace = True
)

# Output IDs
df['zipcode_ordered_id'] = df.zipcode_ordered.cat.codes
print(df)
#  zipcode_category zipcode_ordered  zipcode_ordered_id
#            90210           90210                   1
#            90211           90211                   0

More details on setting ordered categories can be found at the pandas website:

https://pandas.pydata.org/pandas-docs/stable/user_guide/categorical.html#sorting-and-order

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