How to create dummy variable for specifc values in a column?

Question

I want to create a dummy variable for a specific value in a column. Let's say my database looks like this :

I want a dummy variable just for the museums.

pd.get_dummies (df,['Buildings']) 

gives me a dummy for "cinema", "school" and "university". In practice, I could drop the new columns for "cinema", "school" and "university" but only keep the one for "museum" but what if the variable "buildings" takes a lot of values (more than 100) ? What would be the correct syntax to only select a specific value and create with it a dummy variable ?

Answer 1

If need only one column simpliest is create it manually with casting boolean to integers:

df['museum'] = df['Buildings'].eq('museum').astype(int)

With your solution is possible replace non museum values to missing values, then pd.get_dummies omit missing values:

df=pd.DataFrame({'Buildings':['museum','cinema','school']})

print (df)
  Buildings
0    museum
1    cinema
2    school

df1 = df.assign(Buildings = df['Buildings'].where(df['Buildings'].eq('museum')))
out = pd.get_dummies(df1,['Buildings'])
print (out)
   Buildings_museum
0                 1
1                 0
2                 0