### Jürgen Kampf
### Stochastics III
### Introduction in Vectors and Data Frames
### Part 2: Solution
x$Year[x$Day.Temperature>20]
# Explanation:
x$Day.Temperature
# returns the vectors of the Day Temperatures. So the Boolean vector
x$Day.Temperature>20
# is TRUE at those positions, where the day temperature is larger than 20.
# The solution extracts from the vector
x$Year
# only those elements for which
x$Day.Temperature>20
# is TRUE, in other words only those elements, for which the day temperature
# is larger than 20.