How to generate pandas DataFrame column of Categorical from string column?

Question

I can convert a pandas string column to Categorical, but when I try to insert it as a new DataFrame column it seems to get converted right back to Series of str:

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Answer 1

The only workaround for pandas pre-0.15 I found is as follows:

• column must be converted to a Categorical for classifier, but numpy will immediately coerce the levels back to int, losing the factor information
• so store the factor in a global variable outside the dataframe

.

train_LocationNFactor = pd.Categorical.from_array(train['LocationNormalized']) # default order: alphabetical

train['LocationNFactor'] = train_LocationNFactor.labels # insert in dataframe

[UPDATE: pandas 0.15+ added decent support for Categorical]