ST 308

How many rows and columns does the built-in iris dataset have? Hint: Use one of the functions that help you understand your R objects.

150 rows, 5 columns

Suppose you have a numeric vector with elements 1, 2, and 3, in that order. Call this vector x. Suppose you also have a numeric vector with elements 4 and 5, in that order. Call this vector y. What would the result of x+y be?

5

what is the syntax used to store the output of some code in an R object?

<-

What is a list?

A one-dimensional object whose elements can be heterogeneous

What is the class of the letters object?

Character

Why are lists considered one-dimensional when they can contain data frames (which are two-dimensional) within them?

Each element of a list can be any R object but we associate a one-dimensional ordering with these elements

Suppose you ran the code below: final_answer <- log(2.1*4.6/1.9) - 2*exp(4)final_answer TRUE or FALSE: Each time you type final_answer into the console, R has to execute the log and exp functions.

False

True or False R and RStudio are the same software.

False

If you look at the help file for a function and see an argument in the function definition with an = sign and a value next to it, for example runif(n, min = 0, max = 1), what does the value to the right of the equal sign represent?

If the user doesn't specify a value for that argument, this is the default value to use

What is an atomic vector in R?

One dimensional object whose elements are all the same type

How does R do basic mathematical operations on a vector (or numeric data frame)? That is, if I have a numeric vector called vec and run the code vec*10, how does R execute the multiplication?

R applies the operation element-wise

In the above console, type print(cars) on one line and print(exp) on another. Submit the code. Why does print(cars) produce a different type of output than print(exp)?

R is determining how to use print() based on the type of object used as the input

How do data frames and tibbles differ in behavior?

Tibbles do not simplify when subsetting only a single column when using [ , ] tibbles print more nicely than data frames.

mtcars is a built in data set in R. You can obtain the column names of a data frame using the names() function. True or false: gear is one of the columns.

True

What is a delimiter?

a character that separates data values in a raw data file

What is the purpose of the R console?

code is submitted to be evaluated

the console is where?

code is submitted to be evaluated

What function can help you determine your working directory?

getwd()

If you want to look at the help documentation for the "hist" function, what code can you submit to the console?

help(hist)

How does the read_csv function determine column types when reading in a dataset? Hint: Check the help file for the read_csv function and look at the description of the col_types argument.

it imputes column types from the first 1000 rows of the dataset it uses a vector of col_types if it is provided by the user

What function creates a data frame?

list()

Give the syntax for subsetting (returning) the entire 3rd row of a data frame called myDF.

myDF$[3,]

suppose we create a list called myList as follows: myList <- list('first' = iris, 'second'=1:3) What is one way to access the second element of myList and have it be returned as a vector?

myList[[2]]

Installing a package should be done

once on each computer, generally

How can you return more than one element from a vector?

provide an indexing vector with the [] function, for instance, vec[c(3,5,10)]

What will read an R package into your session?

require() library()

Write the R syntax for printing out a sequence of numbers from 1 to 21, by increments of 4. Do not include any spaces in your submission.

seq(from=1, to=21, by=4)

What is the name of the R function we discussed that will compactly display the internal structure of an R object?

str