Exercise

# Transforming raw data

In the last chapter, you calculated the rolling mean. In this exercise, you will define a function that calculates the percent change of the latest data point from the mean of a window of previous data points. This function will help you calculate the percent change over a rolling window.

This is a more stable kind of time series that is often useful in machine learning.

Instructions

**100 XP**

- Define a
`percent_change`

function that takes an input time series and does the following:- Extract all but the last value of the input series (assigned to
`previous_values`

) and the*only the last*value of the timeseries ( assigned to`last_value`

) - Calculate the percentage difference between the last value and the mean of earlier values.

- Extract all but the last value of the input series (assigned to
- Using a rolling window of 20, apply this function to
`prices`

, and visualize it using the given code.