Reindexing DataFrame from a list

Sorting methods are not the only way to change DataFrame Indexes. There is also the .reindex() method.

In this exercise, you'll reindex a DataFrame of quarterly-sampled mean temperature values to contain monthly samples (this is an example of upsampling or increasing the rate of samples, which you may recall from the pandas Foundations course).

The original data has the first month's abbreviation of the quarter (three-month interval) on the Index, namely Apr, Jan, Jul, and Sep. This data has been loaded into a DataFrame called weather1 and has been printed in its entirety in the IPython Shell. Notice it has only four rows (corresponding to the first month of each quarter) and that the rows are not sorted chronologically.

You'll initially use a list of all twelve month abbreviations and subsequently apply the .ffill() method to forward-fill the null entries when upsampling. This list of month abbreviations has been pre-loaded as year.

Instructions

Reorder the rows of weather1 using the .reindex() method with the list year as the argument, which contains the abbreviations for each month.
Reorder the rows of weather1 just as you did above, this time chaining the .ffill() method to replace the null values with the last preceding non-null value.

Take Hint (-30xp)