Measuring Overall ETFs Performance

We will now plot a graph to show the accumulated returns of the ETFs over a period of time.  We can do so by following the following steps:

• Build a dataframe with the 4 ETFs prices and a date column. Calculate daily returns and cumulative returns. The cumsum() function returns the cumulative sums (i.e. the sum of all values up to a certain position of a vector).
• Change the format of the data from wide shape to long shape with the gather() function from dplyr package.
• Use ggplot2 to graph the ETFs performance in the whole period.