Chapter 15

Introduction

Creating Factors

General Social Survey

unordered factor levels

tvhours_by_relig <- gss_cat %>%
    
    group_by(relig) %>%
    summarize(
        avg_tvhours = mean(tvhours, na.rm = TRUE)
    )

tvhours_by_relig
## # A tibble: 15 × 2
##    relig                   avg_tvhours
##    <fct>                         <dbl>
##  1 No answer                      2.72
##  2 Don't know                     4.62
##  3 Inter-nondenominational        2.87
##  4 Native american                3.46
##  5 Christian                      2.79
##  6 Orthodox-christian             2.42
##  7 Moslem/islam                   2.44
##  8 Other eastern                  1.67
##  9 Hinduism                       1.89
## 10 Buddhism                       2.38
## 11 Other                          2.73
## 12 None                           2.71
## 13 Jewish                         2.52
## 14 Catholic                       2.96
## 15 Protestant                     3.15
tvhours_by_relig %>%
    ggplot(aes(x = avg_tvhours, y = relig)) +
    geom_point()

ordered factor levels

tvhours_by_relig %>%
    
    ggplot(aes(x = avg_tvhours, y = fct_reorder(.f = relig, .x = avg_tvhours))) +
    geom_point() +
    
    labs(y = NULL, x = "Mean Daily Hours Watching TV")

Moving a single level to the front

tvhours_by_relig %>%
    
    ggplot(aes(x = avg_tvhours,
               y = fct_reorder(.f = relig, .x = avg_tvhours) %>%
                   fct_relevel("Don't Know"))) +
    geom_point() +
    
    labs(y = NULL, x = "Mean Daily Hours Watching TV")
## Warning: 1 unknown level in `f`: Don't Know

Modifying Factor Order

gss_cat %>% distinct(race)
## # A tibble: 3 × 1
##   race 
##   <fct>
## 1 White
## 2 Black
## 3 Other
gss_cat %>%
    
    mutate(race_rev = fct_recode(race, "African American" = "Black")) %>%
    select(race, race_rev) %>%
    filter(race == "Black")
## # A tibble: 3,129 × 2
##    race  race_rev        
##    <fct> <fct>           
##  1 Black African American
##  2 Black African American
##  3 Black African American
##  4 Black African American
##  5 Black African American
##  6 Black African American
##  7 Black African American
##  8 Black African American
##  9 Black African American
## 10 Black African American
## # ℹ 3,119 more rows
gss_cat %>%
    
    mutate(race_col = fct_collapse(race, "Minority" = c("Black", "Other"))) %>%
    select(race, race_col) %>%
    filter(race != "White")
## # A tibble: 5,088 × 2
##    race  race_col
##    <fct> <fct>   
##  1 Black Minority
##  2 Black Minority
##  3 Black Minority
##  4 Other Minority
##  5 Black Minority
##  6 Other Minority
##  7 Black Minority
##  8 Other Minority
##  9 Black Minority
## 10 Black Minority
## # ℹ 5,078 more rows
gss_cat %>% count(race)
## # A tibble: 3 × 2
##   race      n
##   <fct> <int>
## 1 Other  1959
## 2 Black  3129
## 3 White 16395
gss_cat %>% mutate(race_lump = fct_lump(race)) %>% distinct(race_lump)
## # A tibble: 2 × 1
##   race_lump
##   <fct>    
## 1 White    
## 2 Other

Modifying Factor levels

Chapter 16

Introduction

Creating Dates and Times

"2026-11-09" %>% ymd()
## [1] "2026-11-09"
20261109 %>% ymd()
## [1] "2026-11-09"
"2026-11-09 8-13-30" %>% ymd_hms()
## [1] "2026-11-09 08:13:30 UTC"

Individual Components

flights %>%
    select(year:day, hour, minute) %>%
    mutate(departure = make_datetime(year = year, month = month, day = day, hour = hour, min = minute))
## # A tibble: 336,776 × 6
##     year month   day  hour minute departure          
##    <int> <int> <int> <dbl>  <dbl> <dttm>             
##  1  2013     1     1     5     15 2013-01-01 05:15:00
##  2  2013     1     1     5     29 2013-01-01 05:29:00
##  3  2013     1     1     5     40 2013-01-01 05:40:00
##  4  2013     1     1     5     45 2013-01-01 05:45:00
##  5  2013     1     1     6      0 2013-01-01 06:00:00
##  6  2013     1     1     5     58 2013-01-01 05:58:00
##  7  2013     1     1     6      0 2013-01-01 06:00:00
##  8  2013     1     1     6      0 2013-01-01 06:00:00
##  9  2013     1     1     6      0 2013-01-01 06:00:00
## 10  2013     1     1     6      0 2013-01-01 06:00:00
## # ℹ 336,766 more rows

From Other types

today() %>% as_datetime()
## [1] "2026-11-11 UTC"
now() %>% as_date()
## [1] "2026-11-11"

Date and time components

Getting Components

date_time <- ymd_hms("2026-11-09 8-13-30")
date_time
## [1] "2026-11-09 08:13:30 UTC"
year(date_time)
## [1] 2026
month(date_time, label = TRUE, abbr = FALSE)
## [1] November
## 12 Levels: January < February < March < April < May < June < ... < December
yday(date_time)
## [1] 313
mday(date_time)
## [1] 9
wday(date_time, label = TRUE, abbr = FALSE)
## [1] Monday
## 7 Levels: Sunday < Monday < Tuesday < Wednesday < Thursday < ... < Saturday
make_datetime_100 <- function(year, month, day, time) {
    make_datetime(year, month, day, time %/% 100, time %% 100)
}

flights_dt <- flights %>%
    filter(!is.na(dep_time), !is.na(arr_time)) %>%
    mutate(
        dep_time = make_datetime_100(year, month, day, dep_time),
        arr_time = make_datetime_100(year, month, day, arr_time),
        sched_dep_time = make_datetime_100(year, month, day, sched_dep_time),
        sched_arr_time = make_datetime_100(year, month, day, sched_arr_time)
    ) %>%
    select(origin, dest, ends_with("delay"), ends_with("time"))
flights_dt %>%
    
    transmute(wday = wday(dep_time, label = TRUE)) %>%
    
    ggplot(aes(wday)) +
    geom_bar()

Rounding

flights_dt %>%
    
    mutate(week = ceiling_date(dep_time, "month")) %>%
    select(dep_time, week) %>%
    sample_n(10)
## # A tibble: 10 × 2
##    dep_time            week               
##    <dttm>              <dttm>             
##  1 2013-03-16 12:58:00 2013-04-01 00:00:00
##  2 2013-03-28 14:59:00 2013-04-01 00:00:00
##  3 2013-06-17 21:11:00 2013-07-01 00:00:00
##  4 2013-05-16 10:30:00 2013-06-01 00:00:00
##  5 2013-06-15 18:43:00 2013-07-01 00:00:00
##  6 2013-08-11 19:20:00 2013-09-01 00:00:00
##  7 2013-05-28 18:49:00 2013-06-01 00:00:00
##  8 2013-12-13 07:02:00 2014-01-01 00:00:00
##  9 2013-09-15 20:55:00 2013-10-01 00:00:00
## 10 2013-05-12 13:42:00 2013-06-01 00:00:00
flights_dt %>%
    
    mutate(week = floor_date(dep_time, "month")) %>%
    select(dep_time, week) %>%
    slice(2000:2010)
## # A tibble: 11 × 2
##    dep_time            week               
##    <dttm>              <dttm>             
##  1 2013-01-03 09:11:00 2013-01-01 00:00:00
##  2 2013-01-03 09:12:00 2013-01-01 00:00:00
##  3 2013-01-03 09:12:00 2013-01-01 00:00:00
##  4 2013-01-03 09:13:00 2013-01-01 00:00:00
##  5 2013-01-03 09:14:00 2013-01-01 00:00:00
##  6 2013-01-03 09:14:00 2013-01-01 00:00:00
##  7 2013-01-03 09:16:00 2013-01-01 00:00:00
##  8 2013-01-03 09:17:00 2013-01-01 00:00:00
##  9 2013-01-03 09:23:00 2013-01-01 00:00:00
## 10 2013-01-03 09:23:00 2013-01-01 00:00:00
## 11 2013-01-03 09:23:00 2013-01-01 00:00:00

Setting Components

flights_dt %>%
    mutate(dep_hour = update(dep_time, yday = 1)) %>%
    select(dep_time, dep_hour) %>%
    sample_n(10)
## # A tibble: 10 × 2
##    dep_time            dep_hour           
##    <dttm>              <dttm>             
##  1 2013-10-31 12:50:00 2013-01-01 12:50:00
##  2 2013-07-16 07:40:00 2013-01-01 07:40:00
##  3 2013-12-22 14:31:00 2013-01-01 14:31:00
##  4 2013-11-07 07:49:00 2013-01-01 07:49:00
##  5 2013-07-12 17:19:00 2013-01-01 17:19:00
##  6 2013-02-26 08:07:00 2013-01-01 08:07:00
##  7 2013-04-29 06:24:00 2013-01-01 06:24:00
##  8 2013-03-18 07:06:00 2013-01-01 07:06:00
##  9 2013-11-28 06:35:00 2013-01-01 06:35:00
## 10 2013-11-24 12:57:00 2013-01-01 12:57:00

Time Spans