Merging two pandas dataframes results in “duplicate” columns

Question

I\'m trying to merge two dataframes which contain the same key column. Some of the other columns also have identical headers, although not an equal number of rows, and after

Answer 1

I have the same problem with duplicate columns after left joins even when the columns' data is identical. I did a query and found out that NaN values are considered different even if both columns are NaN in pandas 0.14. BUT once you upgrade to 0.15, this problem disappears, which explains why it later works for you, you probably upgraded.