A list of length seven, elements of which are objects of the class
returns. The list contains all necessary returns from 2019-04-01 to
2020-04-01 of seven companies, which could profit from COVID-19 lockdown. See
examples of apply_market_model for the dataset generation.
securities_returns
A list of eight zoo elements:
AMZN
ZM
UBER
NFLX
SHOP
FB
UPWK