Thank you. Your submission for this quiz was received.
You submitted this quiz on Sun 12 Apr 2015 1:40 AM PDT. You got a score of 20.00 out of 20.00.
###Introduction
This first quiz will check your ability to
execute basic operations on objects in R and to understand some basic concepts. For questions 11–20 you will need to load a dataset
into R and do some basic manipulations in order to answer the questions on the quiz.
You may want to print a copy of the quiz questions to look at as you work on the
assignment. It is recommended that you save your answers as you go in the event that a technical problem should occur with your network connection or computer. Ultimately, you must submit the quiz online to get credit!
The zip file containing the data for questions 11–20 in this Quiz can be downloaded
here:
For this assignment you will need to unzip this file in your working
directory.
<div class="course-quiz-question-body">
R was developed by statisticians working at
| Your Answer |
|
Score |
Explanation |
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The University of New South Wales |
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Insightful |
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The University of Auckland |
Correct |
1.00 |
The R language was developed by Ross Ihaka and Robert Gentleman who were statisticians at the University of Auckland in New Zealand. |
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Microsoft |
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| Total |
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1.00 / 1.00 |
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The definition of free software consists of four freedoms (freedoms 0 through 3). Which of the following is NOT one of the freedoms that are part of the definition?
| Your Answer |
|
Score |
Explanation |
|
The freedom to restrict access to the source code for the software. |
Correct |
1.00 |
This is not part of the free software definition. Freedoms 1 and 3 require access to the source code. |
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The freedom to improve the program, and release your improvements to the public, so that the whole community benefits. |
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The freedom to run the program, for any purpose. |
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The freedom to study how the program works, and adapt it to your needs. |
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| Total |
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1.00 / 1.00 |
|
In R the following are all atomic data types EXCEPT
| Your Answer |
|
Score |
Explanation |
|
character |
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integer |
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numeric |
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table |
Correct |
1.00 |
'table' is not an atomic data type in R. |
| Total |
|
1.00 / 1.00 |
|
If I execute the expression x <- 4 in R, what is the class of the object `x' as determined by the `class()' function?
| Your Answer |
|
Score |
Explanation |
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complex |
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vector |
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numeric |
Correct |
1.00 |
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real |
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| Total |
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1.00 / 1.00 |
|
What is the class of the object defined by the expression x <- c(4, "a", TRUE)?
| Your Answer |
|
Score |
Explanation |
|
character |
Correct |
1.00 |
The character class is the "lowest common denominator" here and so all elements will be coerced into that class. |
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integer |
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mixed |
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numeric |
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| Total |
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1.00 / 1.00 |
|
Question Explanation
R does automatic coercion of vectors so that all elements of the vector are the same data class.
If I have two vectors x <- c(1,3, 5) and y <- c(3, 2, 10), what is produced by the expression rbind(x, y)?
| Your Answer |
|
Score |
Explanation |
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a 3 by 3 matrix |
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a vector of length 2 |
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a vector of length 3 |
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a matrix with two rows and three columns |
Correct |
1.00 |
The 'rbind' function treats vectors as if they were rows of a matrix. It then takes those vectors and binds them together row-wise to create a matrix. |
| Total |
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1.00 / 1.00 |
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A key property of vectors in R is that
| Your Answer |
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Score |
Explanation |
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the length of a vector must be less than 32,768 |
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a vector cannot have have attributes like dimensions |
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elements of a vector can only be character or numeric |
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elements of a vector all must be of the same class |
Correct |
1.00 |
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| Total |
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1.00 / 1.00 |
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Suppose I have a list defined as x <- list(2, "a", "b", TRUE). What does x[[2]] give me?
| Your Answer |
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Score |
Explanation |
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a list containing character vector with the letter "a". |
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a list containing a character vector with the elements "a" and "b". |
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a character vector with the elements "a" and "b". |
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a character vector containing the letter "a". |
Correct |
1.00 |
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| Total |
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1.00 / 1.00 |
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Suppose I have a vector x <- 1:4 and y <- 2:3. What is produced by the expression x + y?
| Your Answer |
|
Score |
Explanation |
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an integer vector with the values 3, 5, 5, 7. |
Correct |
1.00 |
|
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a numeric vector with the values 1, 2, 5, 7. |
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a warning |
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a numeric vector with the values 3, 5, 3, 4. |
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| Total |
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1.00 / 1.00 |
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Suppose I have a vector x <- c(3, 5, 1, 10, 12, 6) and I want to set all elements of this vector that are less than 6 to be equal to zero. What R code achieves this?
| Your Answer |
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Score |
Explanation |
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x[x == 0] |
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x[x <= 5] <- 0 |
Correct |
1.00 |
You can create a logical vector with the expression x <= 5 and then use the [ operator to subset the original vector x. |
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x[x > 0] <- 6 |
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x[x == 6] <- 0 |
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| Total |
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1.00 / 1.00 |
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In the dataset provided for this Quiz, what are the column names of the dataset?
| Your Answer |
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Score |
Explanation |
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1, 2, 3, 4, 5, 6 |
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Ozone, Solar.R, Wind, Temp, Month, Day |
Correct |
1.00 |
You can get the column names of a data frame with the `names()' function. |
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Month, Day, Temp, Wind |
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Ozone, Solar.R, Wind |
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| Total |
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1.00 / 1.00 |
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Extract the first 2 rows of the data frame and print them to the console. What does the output look like?
| Your Answer |
|
Score |
Explanation |
Ozone Solar.R Wind Temp Month Day
1 41 190 7.4 67 5 1
2 36 118 8.0 72 5 2
|
Correct |
1.00 |
You can extract the first two rows using the [ operator and an integer sequence to index the rows. |
Ozone Solar.R Wind Temp Month Day
1 7 NA 6.9 74 5 11
2 35 274 10.3 82 7 17
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Ozone Solar.R Wind Temp Month Day
1 9 24 10.9 71 9 14
2 18 131 8.0 76 9 29
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Ozone Solar.R Wind Temp Month Day
1 18 224 13.8 67 9 17
2 NA 258 9.7 81 7 22
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| Total |
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1.00 / 1.00 |
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How many observations (i.e. rows) are in this data frame?
| Your Answer |
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Score |
Explanation |
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160 |
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129 |
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153 |
Correct |
1.00 |
You can use the `nrow()' function to compute the number of rows in a data frame. |
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45 |
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| Total |
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1.00 / 1.00 |
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Extract the last 2 rows of the data frame and print them to the console. What does the output look like?
| Your Answer |
|
Score |
Explanation |
Ozone Solar.R Wind Temp Month Day
152 18 131 8.0 76 9 29
153 20 223 11.5 68 9 30
|
Correct |
1.00 |
The `tail()' function is an easy way to extract the last few elements of an R object. |
Ozone Solar.R Wind Temp Month Day
152 34 307 12.0 66 5 17
153 13 27 10.3 76 9 18
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Ozone Solar.R Wind Temp Month Day
152 11 44 9.7 62 5 20
153 108 223 8.0 85 7 25
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Ozone Solar.R Wind Temp Month Day
152 31 244 10.9 78 8 19
153 29 127 9.7 82 6 7
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| Total |
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1.00 / 1.00 |
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What is the value of Ozone in the 47th row?
| Your Answer |
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Score |
Explanation |
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63 |
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18 |
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34 |
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21 |
Correct |
1.00 |
The single bracket [ operator can be used to extract individual rows of a data frame. |
| Total |
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1.00 / 1.00 |
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How many missing values are in the Ozone column of this data frame?
| Your Answer |
|
Score |
Explanation |
|
78 |
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37 |
Correct |
1.00 |
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9 |
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43 |
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| Total |
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1.00 / 1.00 |
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Question Explanation
The `is.na' function can be used to test for missing values.
What is the mean of the Ozone column in this dataset? Exclude missing values (coded as NA) from this calculation.
| Your Answer |
|
Score |
Explanation |
|
31.5 |
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18.0 |
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42.1 |
Correct |
1.00 |
|
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53.2 |
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| Total |
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1.00 / 1.00 |
|
Question Explanation
The `mean' function can be used to calculate the mean.
Extract the subset of rows of the data frame where Ozone values are above 31 and Temp values are above 90. What is the mean of Solar.R in this subset?
| Your Answer |
|
Score |
Explanation |
|
212.8 |
Correct |
1.00 |
|
|
185.9 |
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205.0 |
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334.0 |
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| Total |
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1.00 / 1.00 |
|
Question Explanation
You need to construct a logical vector in R to match the question's requirements. Then use that logical vector to subset the data frame.
What is the mean of "Temp" when "Month" is equal to 6?
| Your Answer |
|
Score |
Explanation |
|
79.1 |
Correct |
1.00 |
|
|
75.3 |
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90.2 |
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85.6 |
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| Total |
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1.00 / 1.00 |
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What was the maximum ozone value in the month of May (i.e. Month = 5)?
| Your Answer |
|
Score |
Explanation |
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97 |
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18 |
|
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100 |
|
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115 |
Correct |
1.00 |
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| Total |
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1.00 / 1.00 |
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