将功能应用于数据框列？

Question

I have the following function (one-hot encoding function that takes a column as an input). I basically want to apply it to a column in my dataframe, but can't seem to understand what's going wrong.

def dummies(dataframe, col):
    dataframe[col] = pd.Categorical(dataframe[col])
    pd.concat([dataframe,pd.get_dummies(dataframe[col],prefix = 'c')],axis=1)

df1 = df['X'].apply(dummies)

Guessing something is wrong with how I'm calling it?

Answer 1

you need to make sure you're returning a value from the function, currently you are not..also when you apply a function to a column you are basically passing the value of each row in the column into the function, so your function is set up wrong..typically you'd do it like this:

def function1(value):
    new_value = value*2 #some operation
    return new_value

then:

df['X'].apply(function1)

currently your function is set up to take entire df, and the name of a column, so likely your function might work if you call it like this:

df1 = dummies(df, 'X')

but you still need to add a return statement

Answer 2

If you want to apply it to that one column you don't need to make a new dataframe. This is the correct syntax. Please read the docs .

df['X'] = df['X'].apply(lambda x : dummies(x))