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Loops can execute a block of code as long as a specified condition is reached
Loops can execute a block of code as long as a specified condition is reached.
Loops are handy because they save time, reduce errors, and they make code more readable.
R has two loop commands:
while loopsfor loopsWith the while loop we can execute a set of statements as long as a condition is TRUE:
Print i as long as i is less than 6:
i <- 1
while (i < 6) {
print(i)
i <- i + 1
}
In the example above, the loop will continue to produce numbers ranging from
1 to 5. The loop will stop at 6 because 6 < 6 is FALSE.
The while loop requires relevant variables to be ready, in this example we
need to define an indexing variable, i, which we set to 1.
Note: remember to increment i, or else the loop will continue forever.
With the break statement, we can stop the loop even if the while condition is TRUE:
Exit the loop if i is equal to 4.
i <- 1
while (i < 6) {
print(i)
i <- i + 1
if
(i == 4) {
break
}
}
The loop will stop at 3 because we have chosen to finish the loop by using the break statement when i is equal to 4 (i == 4).
With the next statement, we can skip an iteration without terminating the loop:
Skip the value of 3:
i <- 0
while (i < 6) {
i <- i + 1
if (i == 3) {
next
}
print(i)
}
When the loop passes the value 3, it will skip it and continue to loop.
If .. Else Combined with a While Loop
To demonstrate a practical example, let us say we play a game of Yahtzee!
Print "Yahtzee!" If the dice number is 6:
dice <- 1
while (dice <= 6) {
if (dice < 6) {
print("No
Yahtzee")
} else {
print("Yahtzee!")
}
dice <- dice
+ 1
}
If the loop passes the values ranging from 1 to 5, it prints "No Yahtzee". Whenever it passes the value 6, it prints "Yahtzee!".