Loop over a list
Looping over a list is just as easy and convenient as looping over a vector. There are again two different approaches here:
primes_list <- list(2, 3, 5, 7, 11, 13)
# loop version 1
for (p in primes_list) {
print(p)
}
# loop version 2
for (i in 1:length(primes_list)) {
print(primes_list[[i]])
}
Notice that you need double square brackets - [[ ]] - to select the list elements in loop version 2.
Suppose you have a list of all sorts of information on New York City: its population size, the names of the boroughs, and whether it is the capital of the United States. We've already defined a list nyc containing this information (source: Wikipedia).
This is a part of the course
“Intermediate R”
Exercise instructions
As in the previous exercise, loop over the nyc list in two different ways to print its elements:
- Loop directly over the
nyclist (loop version 1). - Define a looping index and do subsetting using double brackets (loop version 2).
Hands-on interactive exercise
Have a go at this exercise by completing this sample code.
# The nyc list is already specified
nyc <- list(pop = 8405837,
boroughs = c("Manhattan", "Bronx", "Brooklyn", "Queens", "Staten Island"),
capital = FALSE)
# Loop version 1
# Loop version 2