Control Flow

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Learning Objectives

  • next Statements
  • break Statements
  • while Loops

next Statements

  • next Statements

  • break Statements

  • while Loops

  • for Loop Examples

next Statements

The next statement is used to skip an iteration of a loop. This is used along an if statement.

for (i in vector){
  perform task
  if (condition){
    next
  } else {
    perform task
  }
}

break Statements

  • next Statements

  • break Statements

  • while Loops

  • for Loop Examples

break Statements

The break statement is used to stop a loop if the condition is met. This is used along with an if statement.

for (i in vector){
  perform task
  if (condition){
    break
  } else {
    perform task
  }
}

while Loops

  • next Statements

  • break Statements

  • while Loops

  • for Loop Examples

while Loops

A while loop is a combination of a for loop and a break statement. The loop will continue indefinitely until a condition becomes false.

# Initial Condition
condition <- starting TRUE condition

while (condition){
  perform task
  condition <- update condition
}

Example

Simulate from a \(N(0,1)\) distribution until you have 50 positive numbers.

Code 
n <- 0
pos_num <- c()

while (n < 51){
  x <- rnorm(1)
  if (x > 0) {
    pos_num <- c(pos_num, x)
    n <- n + 1
  }
}

pos_num

Example

Find the value of \(x\) where the function \(y=1/x\) relative converges (\(\frac{|y_{old}-y_{new}|}{y_{old}}\)) at a level of \(10^-6\) as \(x\rightarrow \infty\).

Code 
diff <- 10
x <- 2
y_old <- 1
while (diff > 1e-6){
  y_new <- 1 / x
  diff <- abs(y_old - y_new) / y_old
  x <- x + 1
  y_old <- y_new
}

Example

Simulate from a \(Binom(1,.2)\) distribution until the sum of the random variables generated is 50.

Code 
sum_bin <- 0
x <- c()
while (sum_bin <51) {
  x <- c(x, rbinom(1, 1, 0.2))
  sum_bin <- sum(x)
}
sum_bin
length(x)

for Loop Examples

  • next Statements

  • break Statements

  • while Loops

  • for Loop Examples

Example

Generate the 10th row of Pascal’s Triangle.

Code 
i <- 2
x <- c(1, 1)
while (i < 11){
  n <- length(x) + 1
  y <- vector(length = n)
  y[1] <- 1
  y[n] <- 1
  for (i in 2:(n-1)){
    y[i] <- x[i-1] + x[i]
  }
  x <- y
  i <- i + 1
}
x

Example

Generate the first 1000 prime numbers.

Code 
x <- 2
y <- 2
N <- 1
while(N < 1001){
  y <- y + 1
  nn <- length(which(y %% x == 0))
  if (nn == 0){
    x <- c(x,y)
  }
  N <- length(x)
}
x