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To implement complex algorithms and procedures in R, you need to be able to control which instructions to execute and how many times to repeat them.

Conditional Statements

In R, the fundamental conditional structure is based on if and else. The syntax is very similar to languages like JavaScript or C:

score <- 85

if (score >= 60) {
  print("Passed!")
} else {
  print("Failed.")
}

Curly braces {} define the blocks of code to run depending on the outcome of the boolean expression inside parentheses.

The for Loop

The for loop in R is used to iterate over elements in a sequence (such as a vector or list).

# Print numbers from 1 to 3
for (i in 1:3) {
  print(i)
}

In R, the 1:3 syntax is a shorthand way to create the vector c(1, 2, 3).

We can also loop directly over the elements of an existing vector:

fruits <- c("apple", "banana", "cherry")

for (fruit in fruits) {
  print(fruit)
}

The ifelse Function

In R, the ifelse() function is a vectorized version of the if-else statement. It allows you to apply a condition to an entire vector in a single operation, returning a vector of results.

scores <- c(55, 80, 45, 90)
# Se score >= 60 assegna "Pass", altrimenti "Fail"
results <- ifelse(scores >= 60, "Pass", "Fail")
print(results) # "Fail" "Pass" "Fail" "Pass"

The while Loop

The while loop is used to repeat a block of code as long as a specific condition remains true (TRUE). It is essential to ensure that the condition eventually becomes false to prevent infinite loops.

counter <- 1
while (counter <= 3) {
  print(counter)
  counter <- counter + 1
}

Try it yourself