# Sometimes we do not have all the data we want. When that happens, we can represent that in R as missing value, represented as NA.
number.of.pets <-c(2,5,NA,NA)# create a vector that with 2, 5, and two missing values.
# We can use the is.na() function to identify missing data.
unknown.number.of.pets <-is.na(number.of.pets)# Create a variable called unknown.number.of.pets that finds missing data in the variable number.of.pets.