* Character: strings or individual characters, quoted
* Numeric: any real number(s)
* Integer: any integer(s)/whole numbers (1,2,3)
* Double: any number with fractional values (1.2, 4.01, 1.00004)
* Factor: categorical/qualitative variables
* Logical: variables composed of TRUE or FALSE
* Date/POSIXct: represents calendar dates and times

We have already covered character and numeric types.

class(c("tree", "cloud", "stars_&_sky"))

## [1] "character"

class(c(1, 4, 7))

## [1] "numeric"

This can also be a bit tricky.

class(c(1, 2, "tree"))

## [1] "character"

class(c("1", "4", "7"))

## [1] "character"

logical is a type that only has two possible elements: TRUE and FALSE

x <- c(TRUE, FALSE, TRUE, TRUE, FALSE)
class(x)

## [1] "logical"

Note that logical elements are NOT in quotes.

z <- c("TRUE", "FALSE", "TRUE", "FALSE")
class(z)

## [1] "character"

The class of the data tells R how to process the data. For example, it determines whether you can make summary statistics (numbers) or if you can sort alphabetically (characters).

There is one useful functions associated with practically all R classes:

as.CLASS_NAME(x) coerces between classes. It turns x into a certain class.

Examples:

• as.numeric()
• as.character()
• as.logical()
• as.double()
• as.integer()
• as.Date()
• as.factor() (More on this one later!)

Sometimes coercing works great!

as.character(4)

## [1] "4"

as.numeric(c("1", "4", "7"))

## [1] 1 4 7

as.logical(c("TRUE", "FALSE", "FALSE"))

## [1]  TRUE FALSE FALSE

as.logical(0)

## [1] FALSE

When interpretation is ambiguous, R will return NA (an R constant representing “Not Available” i.e. missing value)

as.numeric(c("1", "4", "7a"))

## Warning: NAs introduced by coercion

## [1]  1  4 NA

as.logical(c("TRUE", "FALSE", "UNKNOWN"))

## [1]  TRUE FALSE    NA

What is one reason we might want to convert data to numeric?

A. So we can take the mean

B. So the data looks better

C. So our data is correct

There are two major number subclasses or types:

1. Double (1.003)

2. Integer (1)

Double is equivalent to numeric. It is a number that contains fractional values . Can be any amount of places after the decimal.

Double stands for double-precision

y <- c(1.1, 2.0, 3.21, 4.5, 5.62)
y

## [1] 1.10 2.00 3.21 4.50 5.62

class(y)

## [1] "numeric"

typeof(y)

## [1] "double"

The num function of the tibble package can be used to change format. See here for more: https://tibble.tidyverse.org/articles/numbers.html

Integer is a special number that contains only whole numbers.

y

## [1] 1.10 2.00 3.21 4.50 5.62

y_int <- as.integer(y)
y_int

## [1] 1 2 3 4 5

class(y_int)

## [1] "integer"

typeof(y_int)

## [1] "integer"

Can use as.integer() function to create integers (unless they are read in as integers or created as such with seq and sample). Otherwise, will be double by default.

x <- c(1, 2, 3, 4, 5) # technically integers
class(x)

## [1] "numeric"

typeof(x)

## [1] "double"

A tibble will show the difference (as does glimpse()).

my_data <- tibble(double_var = y, int_var = y_int)
my_data

## # A tibble: 5 × 2
##   double_var int_var
##        <dbl>   <int>
## 1       1.1        1
## 2       2          2
## 3       3.21       3
## 4       4.5        4
## 5       5.62       5

glimpse(my_data)

## Rows: 5
## Columns: 2
## $ double_var <dbl> 1.10, 2.00, 3.21, 4.50, 5.62
## $ int_var    <int> 1, 2, 3, 4, 5

A factor is a special character vector where the elements have pre-defined groups or ‘levels’. You can think of these as qualitative or categorical variables. Order is often important.

Examples:

• red, orange, yellow, green, blue, purple
• breakfast, lunch, dinner
• baby, toddler, child, teen, adult
• Strongly Agree, Agree, Neutral, Disagree, Strongly Disagree
• beginner, novice, intermediate, expert

Use the factor() function to create factors.

x <- c("small", "medium", "large", "medium", "large")
class(x)

## [1] "character"

x_fact <- factor(x)
class(x_fact)

## [1] "factor"

x_fact

## [1] small  medium large  medium large 
## Levels: large medium small

Note that levels are, by default, in alphanumerical order!

Q: Why not use as.factor() ?

A: You can coerce with as.factor(). But you can’t specify levels! More on this soon.

You can learn what are the unique levels of a factor vector

levels(x_fact)

## [1] "large"  "medium" "small"

More on how to change the levels ordering in a lecture coming up!

Factors can be converted to numeric or character very easily.

x_fact

## [1] small  medium large  medium large 
## Levels: large medium small

as.character(x_fact)

## [1] "small"  "medium" "large"  "medium" "large"

as.numeric(x_fact)

## [1] 3 2 1 2 1

Say we want to change daily to be an integer. We would need to use mutate(). Let’s create a new column ‘daily_int’ so it is easier to see what is happening.

circ %>% 
  mutate(daily_int= as.integer(daily)) %>% 
  select(daily, daily_int)

## # A tibble: 1,146 × 2
##    daily daily_int
##    <dbl>     <int>
##  1  952        952
##  2  796        796
##  3 1212.      1211
##  4 1214.      1213
##  5 1644       1644
##  6 1490.      1490
##  7  888.       888
##  8 1000.       999
##  9 1035       1035
## 10 1396.      1395
## # ℹ 1,136 more rows

• There are two types of number class objects: integer and double
• Logic class objects only have TRUE or FALSE (without quotes)
• class() can be used to test the class of an object x
• as.CLASS_NAME(x) can be used to change the class of an object x
• Factors are a special character class that has levels - more on that soon!
• tibbles show column classes!

There are two most popular R classes used when working with dates and times:

• Date class representing a calendar date
• POSIXct class representing a calendar date with hours, minutes, seconds

We convert data from character to Date/POSIXct to use functions to manipulate date/date and time

lubridate is a powerful, widely used R package from “tidyverse” family to work with Date / POSIXct class objects

class("2021-06-15")

## [1] "character"

library(lubridate)

ymd("2021-06-15") # lubridate package Year Month Day

## [1] "2021-06-15"

class(ymd("2021-06-15")) # lubridate package

## [1] "Date"

class(date("2021-06-15")) # lubridate package

## [1] "Date"

Note for function ymd: year month day

mdy("06/15/2021")

## [1] "2021-06-15"

dmy("15-June-2021")

## [1] "2021-06-15"

ymd("2021-06-15")

## [1] "2021-06-15"

Must match the data format!

ymd("06/15/2021") # This doesn't work - gives NA

## Warning: All formats failed to parse. No formats found.

## [1] NA

mdy("06/15/2021") # This works

## [1] "2021-06-15"

a <- ymd("2021-06-15")
b <- ymd("2021-06-18")
a - b

## Time difference of -3 days

class("2013-01-24 19:39:07")

## [1] "character"

ymd_hms("2013-01-24 19:39:07") # lubridate package

## [1] "2013-01-24 19:39:07 UTC"

ymd_hms("2013-01-24 19:39:07") %>% class()

## [1] "POSIXct" "POSIXt"

UTC represents time zone, by default: Coordinated Universal Time

Note for function ymd_hms: year month day hour minute second.

Note dates are always displayed year month day, even if made with mdy!

circ_dates <- circ %>% select(date)
circ_dates <- 
  circ_dates %>% mutate(date_formatted = mdy(date))
glimpse(circ_dates)

## Rows: 1,146
## Columns: 2
## $ date           <chr> "01/11/2010", "01/12/2010", "01/13/2010", "01/14/2010",…
## $ date_formatted <date> 2010-01-11, 2010-01-12, 2010-01-13, 2010-01-14, 2010-0…

circ_dates %>% 
  mutate(year = year(date_formatted)) %>%
  mutate(month = month(date_formatted)) %>% 
  glimpse()

## Rows: 1,146
## Columns: 4
## $ date           <chr> "01/11/2010", "01/12/2010", "01/13/2010", "01/14/2010",…
## $ date_formatted <date> 2010-01-11, 2010-01-12, 2010-01-13, 2010-01-14, 2010-0…
## $ year           <dbl> 2010, 2010, 2010, 2010, 2010, 2010, 2010, 2010, 2010, 2…
## $ month          <dbl> 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1…

Two-dimensional classes are those we would often use to store data read from a file

• a data frame (data.frame or tibble class)
• a matrix (matrix class)
  • also composed of rows and columns
  • unlike data.frame or tibble, the entire matrix is composed of one R class
  • for example: all entries are numeric, or all entries are character

• One other data type that is the most generic are lists.
• Can hold vectors, strings, matrices, models, list of other list!
• Lists are used when you need to do something repeatedly across lots of data - for example wrangling several similar files at once
• Lists are a bit more advanced but you may encounter them when you work with others or look up solutions

Can be created using list()

mylist <- list(c("A", "b", "c"), c(1, 2, 3))
mylist

## [[1]]
## [1] "A" "b" "c"
## 
## [[2]]
## [1] 1 2 3

class(mylist)

## [1] "list"

• coerce between classes using as.numeric() or as.character()
• data frames, tibbles, matrices, and lists are all classes of objects
• lists can contain multiples of any other class of data including lists!
• calendar dates can be represented with the Date class using ymd(), mdy() functions from lubridate package

🏠 Class Website

💻 Lab

📃 Day 4 Cheatsheet See the extra slides for more advanced topics.

Image by Gerd Altmann from Pixabay

as.matrix() creates a matrix from a data frame or tibble (where all values are the same class).

circ_mat <- select(circ, contains("orange")) %>%
  head(n = 3)
circ_mat

## # A tibble: 3 × 3
##   orangeBoardings orangeAlightings orangeAverage
##             <dbl>            <dbl>         <dbl>
## 1             877             1027          952 
## 2             777              815          796 
## 3            1203             1220         1212.

as.matrix(circ_mat)

##      orangeBoardings orangeAlightings orangeAverage
## [1,]             877             1027         952.0
## [2,]             777              815         796.0
## [3,]            1203             1220        1211.5

matrix() creates a matrix from scratch.

matrix(1:6, ncol = 2)

##      [,1] [,2]
## [1,]    1    4
## [2,]    2    5
## [3,]    3    6

List elements can be named

mylist_named <- list(
  letters = c("A", "b", "c"),
  numbers = c(1, 2, 3),
  one_matrix = matrix(1:4, ncol = 2)
)
mylist_named

## $letters
## [1] "A" "b" "c"
## 
## $numbers
## [1] 1 2 3
## 
## $one_matrix
##      [,1] [,2]
## [1,]    1    3
## [2,]    2    4

x <- ymd(c("2021-06-15", "2021-07-15"))
x

## [1] "2021-06-15" "2021-07-15"

day(x) # see also: month(x) , year(x)

## [1] 15 15

x + days(10)

## [1] "2021-06-25" "2021-07-25"

x + months(1) + days(10)

## [1] "2021-07-25" "2021-08-25"

wday(x, label = TRUE)

## [1] Tue Thu
## Levels: Sun < Mon < Tue < Wed < Thu < Fri < Sat

x <- ymd_hms("2013-01-24 19:39:07")
x

## [1] "2013-01-24 19:39:07 UTC"

date(x)

## [1] "2013-01-24"

x + hours(3)

## [1] "2013-01-24 22:39:07 UTC"

floor_date(x, "1 hour") # see also: ceiling_date()

## [1] "2013-01-24 19:00:00 UTC"

x1 <- ymd(c("2021-06-15"))
x2 <- ymd(c("2021-07-15"))

difftime(x2, x1, units = "weeks")

## Time difference of 4.285714 weeks

as.numeric(difftime(x2, x1, units = "weeks"))

## [1] 4.285714

Similar can be done with time (e.g. difference in hours).

n <- 1:9
n

## [1] 1 2 3 4 5 6 7 8 9

mat <- matrix(n, nrow = 3)
mat

##      [,1] [,2] [,3]
## [1,]    1    4    7
## [2,]    2    5    8
## [3,]    3    6    9

To get element(s) of a vector (one-dimensional object):

• Type the name of the variable and open the rectangular brackets [ ]
• In the rectangular brackets, type index (/vector of indexes) of element (/elements) you want to pull. In R, indexes start from 1 (not: 0)

x <- c("a", "b", "c", "d", "e", "f", "g", "h")
x

## [1] "a" "b" "c" "d" "e" "f" "g" "h"

x[2]

## [1] "b"

x[c(1, 2, 100)]

## [1] "a" "b" NA

Note you cannot use dplyr functions (like select) on matrices. To subset matrix rows and/or columns, use matrix[row_index, column_index].

mat

##      [,1] [,2] [,3]
## [1,]    1    4    7
## [2,]    2    5    8
## [3,]    3    6    9

mat[1, 1] # individual entry: row 1, column 1

## [1] 1

mat[1, 2] # individual entry: row 1, column 2

## [1] 4

mat[1, ] # first row

## [1] 1 4 7

mat[, 1] # first column

## [1] 1 2 3

mat[c(1, 2), c(2, 3)] # subset of original matrix: two rows and two columns

##      [,1] [,2]
## [1,]    4    7
## [2,]    5    8

You can reference data from list using $ (if elements are named) or using [[ ]]

mylist_named[[1]]

## [1] "A" "b" "c"

mylist_named[["letters"]] # works only for a list with elements' names

## [1] "A" "b" "c"

mylist_named$letters # works only for a list with elements' names

## [1] "A" "b" "c"