title: Merge and fill two dataframes in Pandas with different time intervals
body: <p>I have two dataframes I'd like to merge in Pandas. They both have a datetime column that I am merging on, however, one has rows every minute and 5 minutes (depending on the year), while the other dataframe has rows every 15 minutes.  If I do an outer join, I can merge them, but only the rows every 15 minutes will have data from both dataframes. I'd like to copy the 15 minute data and fill in each of the 1 or 5 minute rows with this data. So, data from 12:00AM would populate all rows up to and including 12:14AM. Then, 12:15AM would be copied and fill in up to 12:29AM etc.  Does that make sense? How can I accomplish this? <a href="https://stackoverflow.com/questions/27080542/merging-combining-two-dataframes-with-different-frequency-time-series-indexes-in">This question</a> seems similar but I'm not sure how to implement for my exact scenario especially given that my one dataframe changes from 5 minute to 1 minute intervals for different years. </p>