R For Loop
For Loops
A for loop is used for iterating over a sequence:
This is less like the for keyword in other programming languages, and works more like an iterator
method as found in other object-orientated programming languages.
With the for loop we can execute a set of statements, once for each item in a vector,
array, list, etc..
Example
Print every item in a list:
fruits <- list("apple", "banana", "cherry")
for (x in fruits) {
print(x)
}
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Example
Print the number of dices:
dice <- c(1, 2, 3, 4, 5, 6)
for (x in dice) {
print(x)
}
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The for loop does not require an indexing variable to set beforehand, like with while loops.
Break
With the break statement, we can stop the loop before it has looped through all the items:
Example
Stop the loop at "cherry":
fruits <- list("apple", "banana", "cherry")
for (x in fruits) {
if (x == "cherry") {
break
}
print(x)
}
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The loop will stop at "cherry" because we have chosen to finish the loop by using the break statement when
x is equal to "cherry" (x ==
"cherry").
Next
With the next statement, we can skip an iteration without terminating the loop:
Example
Skip "banana":
fruits <- list("apple", "banana", "cherry")
for (x in fruits) {
if (x == "banana") {
next
}
print(x)
}
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When the loop passes "banana", it will skip it and continue to loop.
Yahtzee!
If .. Else Combined with a For Loop
To demonstrate a practical example, let us say we play a game of Yahtzee!
Example
Print "Yahtzee!" If the dice number is 6:
dice <- 1:6
for(x in dice) {
if (x == 6) {
print(paste("The dice number is", x, "Yahtzee!"))
} else {
print(paste("The dice number is", x, "Not Yahtzee"))
}
}
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If the loop reaches the values ranging from 1 to 5, it prints "No Yahtzee" and its number. When it reaches the value 6, it prints "Yahtzee!" and its number.
Nested Loops
A nested loop is a loop inside a loop.
The "inner loop" will be executed one time for each iteration of the "outer loop":
Example
Print the adjective of each fruit in a list:
adj <- list("red", "big", "tasty")
fruits <- list("apple", "banana",
"cherry")
for (x in adj) {
for (y in fruits) {
print(paste(x, y))
}
}
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