For Loop in R Programming

In this lesson, we will discuss the for loop. The syntax of the for loop is:

1for ( name in vector )
2    statement1
3

Here vector can be either a vector or a list. For each element in vector the variable name is set to the value of that element and statement1 is evaluated. Basically, the loop iterates over the vector.

Example: Generate Fibonacci sequence for ‘n’ numbers

The following example shows generating Fibonacci sequence for ‘n’ numbers using the For loop.

1n <- 10
2fib <- numeric(n)
3fib[1] <- 1
4fib[2] <- 1
5for (i in 3:n)
6{
7  fib[i] <- fib[i-1]+fib[i-2] 
8}
9print(fib)
10

The above code will output the Fibonacci series as shown below:

1> print(fib)
2 [1]  1  1  2  3  5  8 13 21 34 55
3

Example: Print Stock Prices

Below is another simple example that prints the stocks prices of a stock from a vector containing stock prices for the past five days.

1stock_A <- c(10, 8, 9, 11, 12)
2for (i in stock_A)
3{
4  print(i)
5}
6

This will print the stock prices one by one as the loop iterates over the elements in the vector:

1[1] 10
2[1] 8
3[1] 9
4[1] 11
5[1] 12
6

Example: Break

The below example demonstrates the use of break statement. For this example, we would like to break and end the loop if the stock price is equal to 11.

1stock_A <- c(10, 8, 9, 11, 12)
2for (i in stock_A)
3{
4  if(i == 11)
5  {
6    break
7  } 
8  print(i)
9}
10

The loop will execute normally. Each time, it will check if i is equal to 11, if not, it will proceed to print the value of i. If i becomes equal to 11, then the break statement will be executed and the loop will be exited.

1[1] 10
2[1] 8
3[1] 9
4