# DataCamp Exercise

It is time for DATA CAMP exercises!

Take your first steps with R. To test your knowledge up to know you can test yourself in the following exercises.

• R makes use of the `#` sign to add comments, so that you and others can understand what the R code is about. Comments are not run as R code, so they will not influence your result. You will find the task written as comment.
• Write directly in the `script.R` window on the left. The comments are telling you what to do.
• When you are ready press `Submit` and every line of code is interpreted and executed by R and you get a message whether or not your code was correct.
• The output of your R code is shown in the `Console` panel on the right.
• Press `Hint` for tips.
• Press `Solution` for a new tab showing the solution.
• `Be patient:` this may take some time to load.
DataCamp Light | Standalone example

## Simple calculation to start:

`# no pec` ``` # Calculate 3 + 4 3 + 4 # Calculate 6 + 12 ``` ``` # Calculate 3 + 4 3 + 4 # Calculate 6 + 12 6 + 12``` ``` test_output_contains("18", incorrect_msg = "Make sure to add `6 + 12` on a new line. Do not start the line with a `#`, otherwise your R code is not executed!") success_msg("Awesome! See how the console shows the result of the R code you submitted? Now that you're familiar with the interface, let's get down to R business!") ```

Just add a line of R code that calculates the sum of 6 and 12, just like the example in the sample code!

## Arithmetic calculations

In its most basic form, R can be used as a simple calculator with the following arithmetic operators:

• Subtraction: -
• Multiplication: *
• Division: /
• Exponentiation: ^
• Modulo: %%

The last two might need some explaining:

The `^` operator raises the number to its left to the power of the number to its right: for example `3^2` is 9.

The modulo `%%` returns the remainder of the division of the number to the left by the number on its right, for example `5 %% 3` is 2.

Instructions:

• Type 5^2 in the editor to calculate 2 to the power 5.
• Type 28 %% 6 to calculate 28 modulo 6.
• Submit the answer and have a look at the R output in the console.
`# no pec` ``` # An addition example 5 + 5 # A subtraction example 5 - 5 # A multiplication example 3 * 5 # A division example 10 / 2 # Exponentiation (5²) # Modulo (28 modulo 6) ``` ``` # An addition 5 + 5 # A subtraction 5 - 5 # A multiplication 3 * 5 # A division 10 / 2 # Exponentiation (5²) 5 ^ 2 # Modulo (28 modulo 6) 28 %% 6 ``` ``` msg = "Do not remove the other arithmetic examples!" test_output_contains("5^2", incorrect_msg = "The exponentiation example is not correct. Write `5 ^ 2` on a new line.") test_output_contains("28 %% 6", incorrect_msg = "There seems to be an issue with the modulo example. Write `28 %% 6` on a new line.") success_msg("Great! Head over to the next exercise.") ```

Another example of the modulo operator: `9 %% 2` equals `1`.

## Assign variables part 1

A basic concept in (statistical) programming is called a variable.

A variable allows you to store a value (e.g. 4) or an object (e.g. a function description) in R. You can then later use this variable's name to easily access the value or the object that is stored within this variable. You can assign a value 4 to a variable with the command `my_var <- 4`.

Instructions:

• Complete the code in the editor such that it assigns the value 42 to the variable x.
• Print x.
`# no pec` ``` # Assign the value 42 to x # Print out the value of the variable x ``` ``` # Assign the value 42 to x x <- 42 # Print out the value of the variable x x ``` ``` test_object("x", undefined_msg = "Make sure to define a variable `x`.", incorrect_msg = "Make sure that you assign the correct value to `x`.") success_msg("Good job! Have you noticed that R does not print the value of a variable to the console when you did the assignment? `x <- 42` did not generate any output, because R assumes that you will be needing this variable in the future. Otherwise you wouldn't have stored the value in a variable in the first place, right? Proceed to the next exercise!") ```

Look at how the value 4 was assigned to `my_variable` in the exercise's assignment. Do the exact same thing in the editor, but now assign 42 to the variable `x`.

## Assign variables part 2

Suppose you have a fruit basket with five apples and you want to store the number of apples in a variable with the name `my_apples`.

Instructions:

• Type the following code in the editor: my_apples <- 5. This will assign the value 5 to my_apples.
• Print my_apples.
`# no pec` ``` # Assign the value 5 to the variable my_apples # Print out the value of the variable my_apples ``` ``` # Assign the value 5 to the variable my_apples my_apples <- 5 # Print out the value of the variable my_apples my_apples ``` ``` test_object("my_apples", undefined_msg = "Please make sure to define a variable `my_apples`.", incorrect_msg = "Make sure that you assign the correct value to `my_apples`.") test_output_contains("my_apples", incorrect_msg = "Have you explicitly told R to print out the `my_apples` variable to the console?") success_msg("Great! Continue to the next exercise!") ```

Remember that if you want to assign a number or an object to a variable in R, you can make use of the assignment operator `<-`. Alternatively, you can use `=`, but `<-` is widely preferred in the R community.

## Assign variables part 3

Every tasty fruit basket needs oranges, so you decide to add six oranges. Your reflex is to immediately create the variable `my_oranges` and assign the value 6 to it. Next, you want to calculate how many pieces of fruit you have in total. Since you have given meaningful names to these values, you can now code this in a clear way: `my_apples + my_oranges`.

Instructions:

• Assign to `my_oranges` the value 6.
• Add the variables `my_apples` and `my_oranges` and have R simply print the result.
• Assign the result of adding my_apples and my_oranges to a new variable `my_fruit`.
`# no pec` ``` # Assign a value to the variables my_apples and my_oranges my_apples <- 5 # Add these two variables together # Create the variable my_fruit ``` ``` # Assign a value to the variables my_apples and my_oranges my_apples <- 5 my_oranges <- 6 # Add these two variables together my_apples + my_oranges # Create the variable my_fruit my_fruit <- my_apples + my_oranges ``` ``` test_object("my_apples", incorrect_msg = "Keep the line that assigns 5 to `my_apples`.") test_object("my_oranges", incorrect_msg = "Keep the line that assigns 6 to `my_oranges`.") test_output_contains("my_apples + my_oranges", incorrect_msg = "Make sure to print out the result of adding `my_apples` and `my_oranges`. The code example in the description already gives away the answer to this instruction!") msg <- "Have you used `my_fruit <- my_apples + my_oranges` to create the `my_fruit` variable?" test_object("my_fruit", undefined_msg = msg, incorrect_msg = msg) success_msg("Nice one! The great advantage of doing calculations with variables is reusability. If you just change `my_apples` to equal 12 instead of 5 and rerun the script, `my_fruit` will automatically update as well. Continue to the next exercise.") ```

`my_fruit` is just the sum of `my_apples` and `my_oranges`. You can use the `+` operator to sum the two and `<-` to assign that value to the variable `my_fruit`.

## Apples and oranges

Common knowledge tells you not to add apples and oranges.
The `my_apples` and `my_oranges` variables both contained a number in the previous exercise. The `+` operator works with numeric variables in R. If you really tried to add "apples" and "oranges", and assigned a text value to the variable `my_oranges` (see the editor), you would be trying to assign the addition of a numeric and a character variable to the variable `my_fruit`. This is not possible.

Instructions:

• Submit the answer and read the error message. Make sure to understand why this did not work.
• Adjust the code so that R knows you have 6 oranges and thus a fruit basket with 11 pieces of fruit.
`# no pec` ``` # Assign a value to the variable my_apples my_apples <- 5 # Fix the assignment of my_oranges my_oranges <- "six" # Create the variable my_fruit and print it out my_fruit <- my_apples + my_oranges my_fruit ``` ``` # Assign a value to the variable my_apples my_apples <- 5 # Fix the assignment of my_oranges my_oranges <- 6 # Create the variable my_fruit and print it out my_fruit <- my_apples + my_oranges my_fruit ``` ``` test_error(incorrect_msg = "You can do this by setting the `my_oranges` variable to a numeric value, not a string!") test_object("my_apples", incorrect_msg = "Make sure that `my_apples` still contains `5`.") test_object("my_oranges", incorrect_msg = "Make sure that `my_oranges` is equal to `6`.") test_object("my_fruit", incorrect_msg = "The value of `my_fruit` is not correct. It should be 11, the sum of `my_apples` and `my_oranges`.") test_output_contains("my_fruit", incorrect_msg = "Don't remove the line that prints out `my_fruit`.") success_msg("Awesome, keep up the good work! Continue to the next exercise.") ```

You have to assign the numeric value `6` to the `my_oranges` variable instead of the character value `"six"`. Note how the quotation marks are used to indicate that `"six"` is a character.

## Basic data types in R

R works with numerous data types. Some of the most basic types to get started are:

• Decimal values like `4.5` are called numerics.
• Whole numbers like `4` are called integers. Integers are also numerics.
• The Boolean values `TRUE` or `FALSE` are called logical.
• Text (or string) values are called characters.
Note how the quotation marks in the editor indicate that `"Apple"` is a string just like `"five"`.

Instructions:

Change the value of the following variables:
• `my_numeric` to 42.
• `my_character` to "universe". Note that the quotation marks indicate that "universe" is a character.
• `my_logical` to FALSE.

Note that R is case sensitive!

`# no pec` ``` # Change my_numeric to be 42 my_numeric <- 42.5 # Change my_character to be "universe" my_character <- "some text" # Change my_logical to be FALSE my_logical <- TRUE ``` ``` # Change my_numeric to be 42 my_numeric <- 42 # Change my_character to be "universe" my_character <- "universe" # Change my_logical to be FALSE my_logical <- FALSE ``` ``` test_object("my_numeric", incorrect_msg = "Have you correctly changed the declaration of `my_numeric` so it contains the value 42?") test_object("my_character", incorrect_msg = "Have you correctly changed `my_character` to `\"universe\"`? Don't forget the quotes!") test_object("my_logical", incorrect_msg = "Have you correctly changed `my_logical` to `FALSE`? All letters of `FALSE` should be capitalized!") success_msg("Great work! Continue to the next exercise.") ```

Replace the values in the editor with the values that are provided in the exercise. For example: `my_numeric <- 42` assigns the value 42 to the variable `my_numeric`.

## What's that data type?

Do you remember that when you added `5 + "six"`, you got an error due to a mismatch in data types? You can avoid such situations by checking the data type of a variable beforehand. You can do this with the `class()` function, as the code in the editor shows.

Instructions:

• Complete the code in the editor and also print out the classes of my_character and my_logical.
`# no pec` ``` # Declare variables of different types my_numeric <- 42 my_character <- "universe" my_logical <- FALSE # Check class of my_numeric class(my_numeric) # Check class of my_character # Check class of my_logical ``` ``` # Declare variables of different types: my_numeric <- 42 my_character <- "universe" my_logical <- FALSE # Check class of my_numeric class(my_numeric) # Check class of my_character class(my_character) # Check class of my_logical class(my_logical) ``` ``` msg <- "Do not change the declaration of the variables!" lapply(c("my_numeric", "my_character", "my_logical"), test_object, undefined_msg = msg, incorrect_msg = msg) patt <- "Have you included `class(%1\$s)` to print out the data type of `%1\$s`?" test_output_contains("class(my_numeric)", incorrect_msg = "Do not remove the code that prints out the type of `my_numeric`.") test_output_contains("class(my_character)", incorrect_msg = sprintf(patt, "my_character")) test_output_contains("class(my_logical)", incorrect_msg = sprintf(patt, "my_logical")) success_msg("Congratulations! This was the last exercise for this chapter. Head over to the next chapter to get immersed in the world of vectors!") ```

The code that prints the data type of `my_numeric` is already included; do a similar things for `my_character` and `my_logical`.

Congratulations! This was the last exercise for this chapter.

Updated: