Lab 1: Getting started with R

Not graded, just practice

To learn to program in R (or any language), you can read about how to do it, and watch someone else do it; but the only way to really learn is to do it yourself. Create some data structures, try some stuff, and see what happens! Here are some practice quiz questions to guide your learning. We will go over the solutions to these in lab.

1 Materials from lab

• Brittany’s lab slides
• Wesley’s lab slides

2 Google Colab

1. True or false? We can start a new R notebook in Google Colab with File > New notebook

   True True, but we need to change the Runtime environment too False

2. For problem sets, how will you submit your colab notebook for grading?

   File > Download > Download .ipynb, then upload to Gradescope File > Download > Download .ipynb, then upload to Canvas File > Download > Download .py, then upload to Gradescope File > Download > Download .py, then upload to Canvas

3. What version of R is Google Colab running? Hint: use sessionInfo().

4. What is the relationship between R and Google Colab?

   R is a programming language. Google Colab is a smaller, specific version of R. R is a programming language. Google Colab is a development environment where you can run R R and Google Colab are both programming languages. R is a paid (proprietary) programming language. Google Colab is a free service to run R.

5. What happens to files you upload to google colab when the Runtime environment is restarted?

   They are saved in your google drive. They are saved in Google Colab's cloud for future use They are deleted They are stored for 7 business days, then deleted.

3 R Basics

1. Which of the following are expressions?

   10 5 + 10 x <- 5 + 10 x <- y + 10 mean(x)

2. Which of the following are valid variable names in R?

   childAge response_time 1stPlaceWinner 2fast2furious pi

3. Suppose we open a new colab notebook and run the following code block. What will be returned?

   x <- 1 + 2
   y <- 0 + 3
   ls()

   3 x=3 • y=3 'x' • 'y' mean(c(1,3,5)) • median(c(1,3,5))

4. Which of the following will load the emo package into the current environment?

   install.packages('emo') library(emo) data(emo) attributes(emo)

5. Which of the following occur in the code block below?

   # compute the mean of x and y
   mean(c(x,y))

   a message a function a comment an expression

4 Vectors

1. Which of the following returns the vector 20 22 24 26

   20:26 seq(from=20, to=26, by =2) rep(c(20, 22, 24, 26), times = 4) c(20, 22, 24, 26)

2. Suppose we construct a vector with c(1, "two", 3, 4, 5, 6) and assign it to x. What will the following code block return?

   typeof(x)

   What is the previous question an example of?

   attribute addition explicit coercion implicit coercion none of the above

3. What will the following code block return?

   x <- 1:4
   y <- matrix(x, ncol=2, nrow=2)
   typeof(y)

4. What will the following code block return?

   x <- c()
   length(x)

5. Given the following output from str(x), what will as.logical(x) return?

   ::: {.cell} ::: {.cell-output .cell-output-stdout}

    num [1:4] 1 0 1 0

   ::: :::

   an error TRUE • FALSE • TRUE • FALSE FALSE FALSE • TRUE • FALSE • TRUE

6. Given the following vector, what will as.double(x) return?

   x <- c("one", "two", "three")

   an error 1 • 2 • 3 2 • 4 • 6 'one' • 'two' • 'three'

7. What happens if you add a vector of numbers to a single number in the following expression?

   c(1, 3, 5) + 1

   2 • 3 • 5 Error: length mismatch 1 • 3 • 5 • 1 2 • 4 • 6

8. What happens if you multiply a vector times another vector?

   c(1, 3, 5) * c(10, 100, 1000)

   10 • 300 • 5000 Error: length mismatch 10 • 30 • 50 • 100 • 300 • 500 • 1000 • 3000 • 5000 a 2 x 3 matrix Error: cannot multiply vectors

9. Suppose we run the following code. What will any(x) return?

   x <- c(1, 5, 11) > 10

   TRUE FALSE Error: vector is double but requires logical

5 Subsetting

1. Which of the following code subsets the vector x <- c("blue", "pink", "red") to return just the first element?

   x[1] x[[1]] x[0] x[-c(2, 3)] x[“blue”]

2. Suppose we run the following code. What will x[[2]] return?

   x <- seq(from = 2, to =8, by=2)

3. Suppose we run the following code. What will m[1, 2] return?

   m <- matrix(c(10,20,30,40), nrow=2, ncol=2)

4. Suppose we run the following code. What will df$y[4] return?

   df <- data.frame(
       x = c(2, 4, 6, 8), 
       y = c("l", "m", "n", "o")
   )

6 Missing Values

1. Suppose we run the following code. What will is.na(y) return?

   
   y <- c(25, 25, NA, 36)

   3 Error: Non-atomic vector is invalid type TRUE FALSE FALSE TRUE FALSE

2. Suppose we run the following code. What will is.null(y) return?

   y <- c()

3. Suppose we run the following code. What will mean(y) return?

   y <- c()