Combining two columns in a dataframe

Question

Let's say I have a dataframe that has, amnog others, two columns, date1, and date2. Date1 is null when date2 is not, and vice-versa.

I want to create a column named "date".

I did this:

def setDate(s1, s2):
    if not isinstance(s1, str):
        return s2
    else:
        return s1

Then, I want to do something like:

data["DATE"] = data[["DATE1", "DATE2"]].apply(lambda x,y : setDate(x,y))

but I keep getting:

TypeError: ("<lambda>() missing 1 required positional argument: 'y'", 'occurred at index DATE1')

How do I use apply on a dataframe to do what I want?

Answer 1

try:

data['DATE'] = pd.to_datetime(data.DATE1.fillna(data.DATE2))

or if you want to keep the dtypes the way they are

data['DATE'] = data.DATE1.fillna(data.DATE2)