TypeError: cannot convert the series to <class 'float'>

You can use lambda operator to apply your functions to the pandas data frame or to the series. More specifically if you want to convert each element on a column to a floating point number, you should do it like this:

df['A'].apply(lambda x: float(x))

here the lambda operator will take the values on that column (as x) and return them back as a float value.

You can use numpy.log instead. Math.log is expecting a single number, not array.