1. When ever we would like to assign an array into a Series, we need to use [[]] instead []
2. double_df = float_df.apply(lambda x: x*2)# use apply() to double each element in the Series
3. The axis argument for apply() is to indicate whether we want to perform the function for each rows or columns. Usually axis = 0 is to apply function to each column. axis = 1 means to apply function to each rows.
原文：http://www.cnblogs.com/kingoscar/p/5947869.html