In thisisdaryn/workshop:

options(htmltools.dir.version = FALSE)
knitr::opts_chunk$set(fig.align="center", fig.width=5, fig.height=5, warning = FALSE, message = FALSE)

library(xaringanthemer)
duo_accent(
  primary_color = "ivory",
  secondary_color = "#310A31",
  header_font_google = google_font("Roboto", "400"),
  text_font_google   = google_font("Lato", "300"),
  code_font_family = "Fira Code",
  code_font_url = "https://cdn.rawgit.com/tonsky/FiraCode/1.204/distr/fira_code.css",
  header_color = "#f54278",
  title_slide_text_color = "#354a66"
)

A note

• These slides make use of the chi_emps data set contained in the workshop package.

library(workshop)
data(chi_emps)

---

Getting summary information

How big is the data set?

dim(chi_emps)

-- What are the names of the columns?

names(chi_emps)

-- You can use summary or View as well to get more info.

---

summary

What happens when you run the following?

summary(chi_emps)

---

summary

What happens when you run the following?

summary(chi_emps)

---

(View)

and what about this?

View(chi_emps)

---

Selecting only some columns

In base R, [] is used to subset data. For a 2d data structure, we have row conditions and column conditions separated by a comma inside the [].

For example, we can select the first 5 rows and the first 4 columns of the chi_emps data frame:

--

chi_emps[c(1:5),c(1:4)]

---

Selecting columns by name

It's often more practical to select columns by name however. The following code: - keeps only the Name, Dept, AnnSalary columns - displays the dimensions of the smaller data set --

chi2 <- chi_emps[, c("Name", "Dept", 
                    "AnnSalary")]
dim(chi2)

-- Note that there was no row constraint in the first line as we were intending to keep all rows of the data.

---

Rows can also be selected using logical operators

How do we select all the rows where the annual salary is in the interquartile range

The code below: - keeps only the rows where the salary is between than $75408 and $97440 - displays the first few rows --

midsal <- chi2[chi2$AnnSalary >= 75408 & chi2$AnnSalary <= 97440, ]
head(midsal)

-- Note that there is no column constraint as we are keeping all the columns.

---

What are the other logical operators that can be used in filtering rows?

The previous slide made use of <, multiple other operators are available for filtering:

Operator <- c( "==", "!=", "<", "<=",  ">", ">=", "|", "&", "!")
Meaning <- c("equal", "not equal", 
             "less than", "less than or equal to", 
              "greater than", "greater than or equal to",
             "Or: at least one of the expressions is true", 
             "And: Both expressions are true", 
             "Not: the expression is not true" )
optable <- data.frame(Operator, Meaning)
kableExtra::kable(optable)

---

Some more examples

How would we get a data set with only hourly paid employees?

hourly <- chi_emps[chi_emps$SalHour == "Hourly", ]

---

Following up on that

How would we get loans that meet both of the following: - have an hourly rate more than $20/hr - typical hours more than 25 --

df <- hourly[(hourly$HourlyRate > 20) & 
               (hourly$TypicalHours > 25), ]
head(df)

---

Another example

How would we get loans that meet either of the following: - the Department is PUBLIC LIBRARY - the employee is Part-time, (FullPart: P)

--

lib_part <- chi_emps[chi_emps$Dept == "PUBLIC LIBRARY" | 
                chi_emps$FullPart == "P", ] 
head(lib_part)

---

Using $ to reference columns

Another means of subsetting data that we would have seen before is the $

hist(chi_emps$HourlyRate)

--

We have been using it to extract single columns from the data

---

$ can be used to create new columns

We can also create new columns in the data set.

For example, here's a new column that says whether or not the interest rate on a loan is greater than 10%:

chi2$sal_gt100 <- ifelse(chi2$AnnSalary > 100000, TRUE, FALSE)
head(chi2)

---

Explaining ifelse

The ifelse function is very handy and has three arguments:

• an expression to evaluate
• a result if the expression is TRUE
• a result if the expression is FALSE

thisisdaryn/workshop documentation built on Jan. 17, 2020, 7:31 p.m.