R-Studio Code for Intro to Statistics, Modules 1-3

Question 1

What is the code used to set the working directory for the RStudio file?

Answer 1

setwd(“C:/Users/Joseph Paoli/Downloads/Lessons in R for Stats/ Module ___”)

Question 2

What is another way to set the working directory in RStudio which involves the lower-right panel of the user interface?
Describe it in three steps.

Answer 2

1. Click the “Files” tab in the lower-right panel, which is next to “Plots”.
2. In the tab below the blue gear, find the correct folder desired for the working directory.
3. Click on the blue gear at this point to open the drop-down menu, then select “Set As Working Directory”.

Question 3

What is the code used to start off RStudio with a blank environment?

Answer 3

rm(list=ls())

Question 4

We want to create a random sequence of 100 numbers, each of which is between 1 and 20, and we want to call this object “random_numbers”.
What is the RScript code to do this?

Answer 4

random_numbers=runif(100, 1, 20)

Question 5

We want to see a summary of the object “random_numbers” (a set of 100 random values between 1 and 20).
What is the RStudio code?

Answer 5

summary(random_numbers)

Question 6

We want to see a histogram of the object “random_numbers” (a set of 100 random values between 1 and 20).
What is the RStudio code?

Answer 6

hist(random_numbers)

Question 7

What six statistics are provided when you run the “summary” command?

Answer 7

Minimum Value
1st Quartile
Median
Mean
3rd Quartile
Maximum Value

Question 8

If we generate a histogram and want to save it as an image file to our working directory, how would we do this?

Answer 8

In the “Plots” tab, select the drop-down menu titled “Export” and select “Save as Image…”, then name the file accordingly.

Question 9

We want to save out the summary statistics from the object “random_numbers”, so that we can use the data to make a table for a later report. We will save it out as an XLS file with the title “rando_values”.
What is the RStudio code to do this?

Answer 9

capture.output(summary(random_numbers), file=”rando_values.xls”)

Question 10

What are the two different ways to call in a dataset in RStudio, assuming the data is in a CSV file format and has the name “TestData.csv”?

Answer 10

1. In the “Environment” tab in the upper-left, select the drop-down menu for “Import Dataset”, then select “From Text (base)…”, at which point a sub-window will open displaying the working directory where the CSV file should be located.
2. We can type the ‘read’ command in the script editor, which would look something like this:
   test_data=read.csv(“TestData.csv”)

Question 11

We have a dataset called “data” which includes nine observations with the following values:
1 1 1 3 5 7 9 14 23
We want to remove all values less than four to create an abbreviated list which is called “modData”.
What is the RStudio code?

Answer 11

modData=data[(data>4)]

Question 12

We want to log-transform the values in the “modData” values.
What is the RStudio code?

Answer 12

log_modData=log(modData)

Question 13

We want to square root-transform the values in the “modData” values.
What is the RStudio code?

Answer 13

sqrt_modData=sqrt(modData)

Question 14

We want to find the average of the set of values in “modData”.
What is the RStudio code?

Answer 14

mean(modData)

Question 15

We want to find the variance of the set of values in “modData”.
What is the RStudio code?

Answer 15

var(modData)

Question 16

We want to find the standard deviation of the set of values in “diam_1983” column of the “tree_diam” data set.

Answer 16

We want to find the standard deviation

Question 17

We want to install and load the package “COBRA” using the RScript Editor. COBRA is a standard set which is found in RStudio at the time of RStudio’s download.
What are the two lines of code in RStudio to do this?

Answer 17

install.packages(“COBRA”)
library(COBRA)

Question 18

Let’s say we have the command “read.table” and we want RStudio to tell us more about how to use it. What is the appropriate code to type in the RScript Editor?

Answer 18

?read.table

Question 19

Let’s say you want to find a code for imputing data into RStudio, but you don’t know that that code might be. What can you type into the RScript Editor which may help?

Answer 19

help.search(“data.input”)

Question 20

Maybe there’s a command like “anova” which you know the name of and want to use, but you don’t know the package it’s located under, so it isn’t loaded in your RStudio session.
What code would locate the package the “anova” command is located in?

Answer 20

find(“anova”)

Question 21

Let’s say we want to run an example of the command “lm”, which generates a linear model of the data, so that we better understand how to perform such analyses and to get familiar with a new command we may not have ever used. What RStudio code could do this for us?

Answer 21

example(lm)

Question 22

What does the RStudio code “demo(graphics)” generate when run?

Answer 22

“demo(graphics)” generates a series of plots and shows the code to make them in the “Console” window in the lower-left.

Given these codes, we can generate similar graphics for our own data by copying and editing the ones provided by the program.

Question 23

What commands return the first and last parts of a vector, matrix, table, data frame or function? For the sake of answering, assume the object has the generic name, “data”.

Answer 23

“head(data)” would give a preview for the first samples in “data”, while “tail(data)” would return the final few samples in “data”.

Question 24

We want to know the names of all the columns in a data set called “tree_diameters”. What is the appropriate RScript code?

Answer 24

colnames(tree_diameters)

Question 25

What two separate commands could we run to produce the number of rows and the number of columns for a data set with the name “tree_diameters” in the console?

Answer 25

nrow(tree_diameters)
ncol(tree_diameters)

Question 26

What single command could we run to produce the number of rows and the number of columns for a data set with the name “tree_diameters” in the console on the same line?

Answer 26

dim(tree_diameters)

Question 27

We want to examine the internal structure of the R object “tree_diameters”. What RScript code can we type?

Answer 27

str(tree_diameters)

Question 28

What RScript code would one type to find the range in values for the data set “tree_diameters” from one particular column which represents those trees sampled in 1983, referred to in the table as “diam_1983”?

Answer 28

range(tree_diameters$diam_1983)

Question 29

What code would we type to produce the 10% quantile for the column “diam_1983” in the “tree_diameters” data set? That is to say, 10% of the other samples are below it and the remaining 90% of samples are above it?

Answer 29

quantile(tree_diameters$diam_1983, 0.1)

Question 30

What code would we type to produce the 90% quantile for the column “diam_1985” in the “tree_diameters” data set? That is to say, 90% of the other samples are below it and the remaining 10% of samples are above it?

Answer 30

quantile(tree_diameters$diam_1985, 0.9)

Question 31

What code would we type to produce the 1%, 50% and 99% quantiles for the column “diam_1987” in the “tree_diam” data set? That is to say, in the console we would obtain the value for the output 1% of observations fall beneath, 50% of observations fall beneath, and 99% of observations fall beneath?

Answer 31

quantile(tree_diam$diam_1987, c(0.01, 0.50, 0.99))

Question 32

We have a column “varieties” in the data set “tree_diameters” which provides the species of the trees present in the study (i.e., ‘‘M.domestica”, “P.armeniaca”, “C.paradisi”, etc.).
What RScript code could we type to succinctly see in the console what all of the species present under “varieties”?

Answer 32

unique(tree_diameters$varieties)

Question 33

What RScript code can we write to tabulate the number of samples we have for each species in the “varieties” column in the “tree_diameters” data set?

Answer 33

table(tree_diameters$varieties)

Question 34

What RScript code can we type to generate all of the integer numbers from one to ten?

Answer 34

indexes=1:10

Question 35

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to modify it so that only the first seven columns appear in a new data set, “tree_diam_mod1”. What RScript code could we write to accomplish this?

Answer 35

indexes_columns=1:7
tree_diam_mod1=tree_diam[, indexes_columns]

Question 36

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to modify it so that only the first nine rows appear in a new data set, “tree_diam_mod2”. What RScript code could we write to accomplish this?

Answer 36

indexes_rows=1:9
tree_diam_mod2=tree_diam[indexes_rows ,]

Question 37

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to modify it so that only the first 11 rows and the first 13 columns appear in a new data set, “tree_diam_mod3”. What RScript code could we write to accomplish this?

Answer 37

indexes_columns=1:13
indexes_rows=1:11
tree_diam_mod3=tree_diam[indexes_rows , indexes_columns]

Question 38

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to modify it so that only the first, third and sixth columns appear in a new data set, “tree_diam_mod4”. What RScript code could we write to accomplish this?

Answer 38

indexes_columns=c(1, 3, 6)
tree_diam_mod4=tree_diam[, indexes_columns]

Question 39

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to modify it so that only the second, fourth and eighth rows appear in a new data set, “tree_diam_mod5”. What RScript code could we write to accomplish this?

Answer 39

indexes_rows=c(2, 4, 8)
tree_diam_mod5=tree_diam[indexes_rows ,]

Question 40

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to exclude the first row to generate the data set “tree_diam_mod6”. What RScript code could we write to accomplish this?

Answer 40

tree_diam_mod6=tree_diam[-1,]

Question 41

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to exclude the first column to generate the data set “tree_diam_mod7”. What RScript code could we write to accomplish this?

Answer 41

tree_diam_mod7=tree_diam[, -1]

Question 42

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to exclude the first, third, and seventh rows to generate the data set “tree_diam_mod8”. What RScript code could we write to accomplish this?

Answer 42

indexes_rows=c(1, 3, 7)
tree_diam_mod8=tree_diam[-indexes_rows,]

Question 43

We have the data set “tree_diam”, which has 4,027 rows and 30 columns. We want to exclude the third, fourth, and ninth columns to generate the data set “tree_diam_mod9”. What RScript code could we write to accomplish this?

Answer 43

indexes_columns=c(3, 4, 9)
tree_diam_mod9=tree_diam[, -indexes_columns]

Question 44

We have the data set “tree_diam”, which has 4,027 rows and 30 columns.
We want to exclude first, third and eighth rows, and we want to remove the second, fifth and ninth columns.
The new data set is to have the name “tree_diam_mod10”.
What RScript code could we write to accomplish this?

Answer 44

indexes_rows=c(1, 3, 8)
indexes_columns=c(2, 5, 9)
tree_diam_mod10=tree_diam[-indexes_rows, -indexes_columns]

Question 45

We have the data set “tree_diam”, which has 4,027 rows and 30 columns.
Two of the columns have the names “species” and “diam_1983”, and we want to exclude the others to generate a new data set with only these two columns and the name “tree_diam_mod11”.
What RScript code could we write to accomplish this?

Answer 45

retain_columns=c(“species”, “diam_1983”)
tree_diam_mod11=tree_diam[, retain_columns]

Question 46

We have generated a histogram after running the code “hist(tree_data$height)”, but we want to spruce it up to have the x-axis label “Tree Species”, the y-axis label “Height (m)”, and the overall title of “Average Height for Given Tree Species”.
What RScript code could we write to accomplish this?

Answer 46

hist(tree_data$height, main = “Average Height for Given Tree Species”,
xlab = “Tree Species”, ylab = “Height (m)”)

Question 47

We want to find the standard deviation for trees in the “diam_1984” column of the “tree_diam” data set. What command can we type in RScript to split the data into subsets, compute summary statistics for each subset, and return the results of those summaries in the console?

Answer 47

aggregate(diam_1984~species, data=tree_diam, sd)