R For Loop
A for loop runs a block once for each value in a sequence. The loop variable takes each value in turn.
Run over a number run
The loop variable takes each number from 1 to 5. Each round prints the current number.
for (n in 1:5) {
print(n)
}Run over day names
The loop variable takes each day name in turn. Each round prints one name.
for (day in c("Mon", "Tue", "Wed")) {
print(day)
}The last value stays
The loop prints each number from 1 to 3. A final print shows the loop variable still holds 3.
for (n in 1:3) {
print(n)
}
print(n)Example
total <- 0
for (n in 1:4) {
total <- total + n
}
print(total)Key points
- The word in joins the loop variable to its values.
- The colon symbol builds a run of numbers such as 1 to 5.
- The values after in decide how many rounds run.
- A for loop suits a known set of values.
- The loop variable keeps its last value after the loop ends.
In this example, the loop runs once for each number from 1 to 4. Each round adds the loop variable to total, and print shows 10.
Try it Yourself
Edit the code, then press Run.
Running is simulated · rdrr.io R Snippets
Exercise
What does the loop variable hold after a loop over 1 to 3 finishes?