# Loops in R – Exercises

**R-exercises**, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)

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Using loops is generally discouraged in R when it is possible to avoid them using *vectorized* alternatives. Vectorized solution are be both faster to write, read and execute – except sometimes they aren’t and the definition of vectorization isn’t always straightforward.

In any event, solutions using loops *can* be:

- The fastest to prototype
- The easiest to understand for people coming from other programming language
- Impossible to avoid – the only way to solve a specific problem.

Furthermore, loops are a great tool to play around with in order to gain a deeper understanding of R.

Solutions are available here.

**Exercise 1**

Write a for loop that iterates over the numbers 1 to 7 and prints the cube of each number using `print()`

.

**Exercise 2**

Write a for loop that iterates over the column names of the inbuilt iris dataset and print each together with the number of characters in the column name in parenthesis. Example output: `Sepal.Length (12)`

. Use the following functions `print()`

, `paste0()`

and `nchar()`

.

**Exercise 3**

Write a *while* loop that prints out standard random normal numbers (use `rnorm()`

) but stops (breaks) if you get a number bigger than 1.

**Exercise 4**

Using `next`

adapt the loop from last exercise so that doesn’t print negative numbers.

**Exercise 5**

Using a for loop simulate the flip a coin twenty times, keeping track of the individual outcomes (1 = heads, 0 = tails) in a vector that you preallocte.

**Exercise 6**

Use a nested for loop (a for loop inside a for loop) that produces the following matrix, preallocate the matrix with `NA`

values.

0 1 2 3 4 1 0 1 2 3 2 1 0 1 2 3 2 1 0 1 4 3 2 1 0

**Exercise 7**

Use a while loop to investigate the number of terms required before the product

1⋅2⋅3⋅4⋅…

reaches above 10 million.

**Exercise 8**

Use a while loop to simulate one stock price path starting at 100 and random normally distributed percentage jumps with mean 0 and standard deviation of 0.01 each period. How long does it take to reach above 150 or below 50?

**Exercise 9**

Implement a simple version of Guess the number game using a while loop. The user should guess a number between 1 and 10, you can use `scan()`

to get user input. The loop should break if the user guesses 5.

**Exercise 10**

Implement a multiplication game. A while loop that gives the user two random numbers from 2 to 12 and asks the user to multiply them. Only exit the loop after five correct answers. Try using `as.integer(readline())`

instead of `scan()`

this time.

If you enjoyed this exercise set you might also enjoy Writing custom functions or Answer probability questions with simulation.

(Image by Nicolas Raymond)

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