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Exercise 1: Hello world

Let's dive in R with an iconic programming example:

Write a simple script to say hello to the world. To do that, first create a variable called greetings and assign it the value Hello world!. Then, print greetings to the screen with the function:

print()
Answer 
greetings <- 'Hello world!'
print(greetings)

Exercise 2: Check the documentation of print

print is not a complicated function, but reading documentation is a good programming habit. Let's check the documentation available for print. To do so, type:

?print

and look at the left panel in RStudio. Try to answer the following questions:

  1. How many named arguments does print have?
  2. How do you control if strings should be print with or without quotes?
Answers
  1. 10
  2. By setting the argument 'quote' to TRUE if quotes are desired and FALSE otherwise.

Exercise 3: Check the basic type of a variable

An easy way to check the type of a given variable is by using the function

class()

Now define the following variables and set them to the values below

a <- 10
b <- FALSE
c <- "Hola mundo"
d <- 10.00

and check the class of all of them.

Answer
  1. numeric
  2. logical
  3. character
  4. numeric

Exercise 4: numeric vs integer

Write the following code

a <- 10.3333
b <- as.integer(a)

Now answer the following questions:

  1. What is the type of a?
  2. What is the type of b?
  3. What's the difference between the values of a and b. Why?
  4. What is as.integer doing?
Answers
  1. Numeric
  2. Integer
  3. A is a numeric type variable whose value is a decimal number.
  4. as.integer is converting a numeric variable into an integer. Since an integer cannot have a fractional component, it is discarded.

Exercise 5: basic calculus

Write a script that:

  1. Calculates and stores the result of: 126 * 37
  2. Checks If the result of 126 * 37 is greater than 4660
Answer 
result     <- 126 * 37
comparison <- (result > 4660)
print(comparison)

Exercise 6: the remainder of the division

Write a script that divides 1600 by 1250 and retrieves the remainder of the operation. Then, check if the remainder is less than 30. Print the result.

Answer 
remainder  <- 1600 %% 1250
comparison <- reminder < 30
print(comparison)

Exercise 7: Randomness madness

We can use runif() to generate random numbers. For instance, to generate a random rational number between 1 and 20, we can type:

a <- runif(min=1, max=20, n=1)

Write a script that uses the aforementioned function to generate three numbers, from 1 to 100, and save them to three variables called first, second and third respectively.

Now check if first is greater than or equal to second. Store the result to a variable called first_vs_second. Print its value.

After that, divide second by third and multiply it by first. Store and print the result.

Answer 
first  <- runif(min=1, max=100, n=1)
second <- runif(min=1, max=100, n=1)
third  <- runif(min=1, max=100, n=1)

first_vs_second <- first >= second
print(first_vs_second)

result <- second / third * first
print(result)

Exercise 8: Order matters

Define in a script the following variables:

a <- 10
b <- 15
d <- 2

Then, write a script that performs the following arithmethic operations:

  1. Sum a and b
  2. Divide the result by d
  3. Print the result

You cannot write more than one line of code for both arithmethic operations.

Answer 
a <- 10
b <- 15
d <- 2

result <- (a + b) / d # One line of code
print(result)

Remember: In programming, arithmethic operators work the same as their mathemathic counterparts. That means that, unless you are using parenthesis, division is performed before sum.