This document discusses different types of loops in R including for loops, while loops, repeat loops, and nested loops. It provides code examples and explanations of how each loop works. For loops are used to iterate over vectors and can iterate by value or index. While loops execute a block of code until a test condition is no longer satisfied. Repeat loops continuously iterate until a break statement is reached. Nested for loops are useful for traversing multi-dimensional data. Finally, apply functions like lapply and sapply implement looping internally to apply functions over lists or arrays.

1. Loops in R
Summer Data Jam

2. Type of Loops
● For loop
● While loop
● ifelse
● Repeat Nested For loop
● Apply Function

3. For Loop
Used to iterate over a vector.

4. Iteration Mode
● By value
#Code Format
for (val in sequence) {
statement
}

5. Example

6. Example
x <- c(2,5,3,9,8,11,6)
for (val in x) {
if(val %% 2 == 0)
print(val)
}

7. By Index

8. Format
for (i in 1:100) {
print(i)
}

9. Example
data <-read.csv(‘kalonzo’)
for (i in 1:nrow(data))
{
print(data$text)[i]
}

10. While Loop
Loop will execute a block of commands until
the condition is no longer satisfied.

11. while (test_expression) {
statement
}

12. Example
i <- 1
while (i < 6) {
print(i)
i = i+1
}

13. Repeat
● A repeat loop is used to iterate over a block of code
multiple number of times.
● There is no condition check in repeat loop to exit the
loop.
● We must ourselves put a condition explicitly inside the
body of the loop.
● Use the break to terminate loop.
● Otherwise produces an infinite loop.
● Similar to while(True)

14. Example
x <- 1
repeat {
print(x)
x = x+1
if (x == 6){
break
}
}

15. Nested For Loop
● Utilised for traversing multiple dimensions
in high-dimensional data.
● Executes outer loop first.

17. Apply Function
A group of functions that internally implement loops.
apply: Function to process array margins
lapply: Loop for a list, to evaluate a function on element
sapply: Similar to lapply but for simple output format.
tapply: function to process vector subsets