Working with Dates

<br>
<br>
.pull-right[

# Working with Dates
## Dr. Mine Dogucu
]

---

```r
library(lubridate)
```

---

---

```r
today()
```

```
## [1] "2020-11-08"
```

```r
now()
```

```
## [1] "2020-11-08 19:46:52 PST"
```

---
class: inverse middle

---

#### `mdy()`

```r
arrival <- c("November 1st, 2005", "February 2nd 2007")
```

```r
str(arrival)
```

```
##  chr [1:2] "November 1st, 2005" "February 2nd 2007"
```

```r
mdy(arrival)
```

```
## [1] "2005-11-01" "2007-02-02"
```

```r
str(mdy(arrival))
```

```
##  Date[1:2], format: "2005-11-01" "2007-02-02"
```

---

```r
mdy("11012005")
```

```
## [1] "2005-11-01"
```

```r
mdy("Nov-01-2005")
```

```
## [1] "2005-11-01"
```

---

`mdy()`

`ymd()`

`dmy()`

---

We can include hours, minutes and seconds too.

```r
mdy_hms("11/01/2005 22:05:18")
```

```
## [1] "2005-11-01 22:05:18 UTC"
```

```r
mdy_hms("11/01/2005 22:05:18") %>% 
  str()
```

```
##  POSIXct[1:1], format: "2005-11-01 22:05:18"
```

---

## Types

`date`

`time`

`date-time`

`POSIXct`

`POSIXlt`

---

## Including time zones

```r
mdy_hms("11/01/2005 22:05:18", 
        tz = "America/Los_Angeles")
```

```
## [1] "2005-11-01 22:05:18 PST"
```

---

## All time zones

```r
OlsonNames()
```

```
##   [1] "Africa/Abidjan"                   "Africa/Accra"                    
##   [3] "Africa/Addis_Ababa"               "Africa/Algiers"                  
##   [5] "Africa/Asmara"                    "Africa/Asmera"                   
##   [7] "Africa/Bamako"                    "Africa/Bangui"                   
##   [9] "Africa/Banjul"                    "Africa/Bissau"                   
##  [11] "Africa/Blantyre"                  "Africa/Brazzaville"              
##  [13] "Africa/Bujumbura"                 "Africa/Cairo"                    
##  [15] "Africa/Casablanca"                "Africa/Ceuta"                    
##  [17] "Africa/Conakry"                   "Africa/Dakar"                    
##  [19] "Africa/Dar_es_Salaam"             "Africa/Djibouti"                 
##  [21] "Africa/Douala"                    "Africa/El_Aaiun"                 
##  [23] "Africa/Freetown"                  "Africa/Gaborone"                 
##  [25] "Africa/Harare"                    "Africa/Johannesburg"             
##  [27] "Africa/Juba"                      "Africa/Kampala"                  
##  [29] "Africa/Khartoum"                  "Africa/Kigali"                   
##  [31] "Africa/Kinshasa"                  "Africa/Lagos"                    
##  [33] "Africa/Libreville"                "Africa/Lome"                     
##  [35] "Africa/Luanda"                    "Africa/Lubumbashi"               
##  [37] "Africa/Lusaka"                    "Africa/Malabo"                   
##  [39] "Africa/Maputo"                    "Africa/Maseru"                   
##  [41] "Africa/Mbabane"                   "Africa/Mogadishu"                
##  [43] "Africa/Monrovia"                  "Africa/Nairobi"                  
##  [45] "Africa/Ndjamena"                  "Africa/Niamey"                   
##  [47] "Africa/Nouakchott"                "Africa/Ouagadougou"              
##  [49] "Africa/Porto-Novo"                "Africa/Sao_Tome"                 
##  [51] "Africa/Timbuktu"                  "Africa/Tripoli"                  
##  [53] "Africa/Tunis"                     "Africa/Windhoek"                 
##  [55] "America/Adak"                     "America/Anchorage"               
##  [57] "America/Anguilla"                 "America/Antigua"                 
##  [59] "America/Araguaina"                "America/Argentina/Buenos_Aires"  
##  [61] "America/Argentina/Catamarca"      "America/Argentina/ComodRivadavia"
##  [63] "America/Argentina/Cordoba"        "America/Argentina/Jujuy"         
##  [65] "America/Argentina/La_Rioja"       "America/Argentina/Mendoza"       
##  [67] "America/Argentina/Rio_Gallegos"   "America/Argentina/Salta"         
##  [69] "America/Argentina/San_Juan"       "America/Argentina/San_Luis"      
##  [71] "America/Argentina/Tucuman"        "America/Argentina/Ushuaia"       
##  [73] "America/Aruba"                    "America/Asuncion"                
##  [75] "America/Atikokan"                 "America/Atka"                    
##  [77] "America/Bahia"                    "America/Bahia_Banderas"          
##  [79] "America/Barbados"                 "America/Belem"                   
##  [81] "America/Belize"                   "America/Blanc-Sablon"            
##  [83] "America/Boa_Vista"                "America/Bogota"                  
##  [85] "America/Boise"                    "America/Buenos_Aires"            
##  [87] "America/Cambridge_Bay"            "America/Campo_Grande"            
##  [89] "America/Cancun"                   "America/Caracas"                 
##  [91] "America/Catamarca"                "America/Cayenne"                 
##  [93] "America/Cayman"                   "America/Chicago"                 
##  [95] "America/Chihuahua"                "America/Coral_Harbour"           
##  [97] "America/Cordoba"                  "America/Costa_Rica"              
##  [99] "America/Creston"                  "America/Cuiaba"                  
## [101] "America/Curacao"                  "America/Danmarkshavn"            
## [103] "America/Dawson"                   "America/Dawson_Creek"            
## [105] "America/Denver"                   "America/Detroit"                 
## [107] "America/Dominica"                 "America/Edmonton"                
## [109] "America/Eirunepe"                 "America/El_Salvador"             
## [111] "America/Ensenada"                 "America/Fort_Nelson"             
## [113] "America/Fort_Wayne"               "America/Fortaleza"               
## [115] "America/Glace_Bay"                "America/Godthab"                 
## [117] "America/Goose_Bay"                "America/Grand_Turk"              
## [119] "America/Grenada"                  "America/Guadeloupe"              
## [121] "America/Guatemala"                "America/Guayaquil"               
## [123] "America/Guyana"                   "America/Halifax"                 
## [125] "America/Havana"                   "America/Hermosillo"              
## [127] "America/Indiana/Indianapolis"     "America/Indiana/Knox"            
## [129] "America/Indiana/Marengo"          "America/Indiana/Petersburg"      
## [131] "America/Indiana/Tell_City"        "America/Indiana/Vevay"           
## [133] "America/Indiana/Vincennes"        "America/Indiana/Winamac"         
## [135] "America/Indianapolis"             "America/Inuvik"                  
## [137] "America/Iqaluit"                  "America/Jamaica"                 
## [139] "America/Jujuy"                    "America/Juneau"                  
## [141] "America/Kentucky/Louisville"      "America/Kentucky/Monticello"     
## [143] "America/Knox_IN"                  "America/Kralendijk"              
## [145] "America/La_Paz"                   "America/Lima"                    
## [147] "America/Los_Angeles"              "America/Louisville"              
## [149] "America/Lower_Princes"            "America/Maceio"                  
## [151] "America/Managua"                  "America/Manaus"                  
## [153] "America/Marigot"                  "America/Martinique"              
## [155] "America/Matamoros"                "America/Mazatlan"                
## [157] "America/Mendoza"                  "America/Menominee"               
## [159] "America/Merida"                   "America/Metlakatla"              
## [161] "America/Mexico_City"              "America/Miquelon"                
## [163] "America/Moncton"                  "America/Monterrey"               
## [165] "America/Montevideo"               "America/Montreal"                
## [167] "America/Montserrat"               "America/Nassau"                  
## [169] "America/New_York"                 "America/Nipigon"                 
## [171] "America/Nome"                     "America/Noronha"                 
## [173] "America/North_Dakota/Beulah"      "America/North_Dakota/Center"     
## [175] "America/North_Dakota/New_Salem"   "America/Nuuk"                    
## [177] "America/Ojinaga"                  "America/Panama"                  
## [179] "America/Pangnirtung"              "America/Paramaribo"              
## [181] "America/Phoenix"                  "America/Port_of_Spain"           
## [183] "America/Port-au-Prince"           "America/Porto_Acre"              
## [185] "America/Porto_Velho"              "America/Puerto_Rico"             
## [187] "America/Punta_Arenas"             "America/Rainy_River"             
## [189] "America/Rankin_Inlet"             "America/Recife"                  
## [191] "America/Regina"                   "America/Resolute"                
## [193] "America/Rio_Branco"               "America/Rosario"                 
## [195] "America/Santa_Isabel"             "America/Santarem"                
## [197] "America/Santiago"                 "America/Santo_Domingo"           
## [199] "America/Sao_Paulo"                "America/Scoresbysund"            
## [201] "America/Shiprock"                 "America/Sitka"                   
## [203] "America/St_Barthelemy"            "America/St_Johns"                
## [205] "America/St_Kitts"                 "America/St_Lucia"                
## [207] "America/St_Thomas"                "America/St_Vincent"              
## [209] "America/Swift_Current"            "America/Tegucigalpa"             
## [211] "America/Thule"                    "America/Thunder_Bay"             
## [213] "America/Tijuana"                  "America/Toronto"                 
## [215] "America/Tortola"                  "America/Vancouver"               
## [217] "America/Virgin"                   "America/Whitehorse"              
## [219] "America/Winnipeg"                 "America/Yakutat"                 
## [221] "America/Yellowknife"              "Antarctica/Casey"                
## [223] "Antarctica/Davis"                 "Antarctica/DumontDUrville"       
## [225] "Antarctica/Macquarie"             "Antarctica/Mawson"               
## [227] "Antarctica/McMurdo"               "Antarctica/Palmer"               
## [229] "Antarctica/Rothera"               "Antarctica/South_Pole"           
## [231] "Antarctica/Syowa"                 "Antarctica/Troll"                
## [233] "Antarctica/Vostok"                "Arctic/Longyearbyen"             
## [235] "Asia/Aden"                        "Asia/Almaty"                     
## [237] "Asia/Amman"                       "Asia/Anadyr"                     
## [239] "Asia/Aqtau"                       "Asia/Aqtobe"                     
## [241] "Asia/Ashgabat"                    "Asia/Ashkhabad"                  
## [243] "Asia/Atyrau"                      "Asia/Baghdad"                    
## [245] "Asia/Bahrain"                     "Asia/Baku"                       
## [247] "Asia/Bangkok"                     "Asia/Barnaul"                    
## [249] "Asia/Beirut"                      "Asia/Bishkek"                    
## [251] "Asia/Brunei"                      "Asia/Calcutta"                   
## [253] "Asia/Chita"                       "Asia/Choibalsan"                 
## [255] "Asia/Chongqing"                   "Asia/Chungking"                  
## [257] "Asia/Colombo"                     "Asia/Dacca"                      
## [259] "Asia/Damascus"                    "Asia/Dhaka"                      
## [261] "Asia/Dili"                        "Asia/Dubai"                      
## [263] "Asia/Dushanbe"                    "Asia/Famagusta"                  
## [265] "Asia/Gaza"                        "Asia/Harbin"                     
## [267] "Asia/Hebron"                      "Asia/Ho_Chi_Minh"                
## [269] "Asia/Hong_Kong"                   "Asia/Hovd"                       
## [271] "Asia/Irkutsk"                     "Asia/Istanbul"                   
## [273] "Asia/Jakarta"                     "Asia/Jayapura"                   
## [275] "Asia/Jerusalem"                   "Asia/Kabul"                      
## [277] "Asia/Kamchatka"                   "Asia/Karachi"                    
## [279] "Asia/Kashgar"                     "Asia/Kathmandu"                  
## [281] "Asia/Katmandu"                    "Asia/Khandyga"                   
## [283] "Asia/Kolkata"                     "Asia/Krasnoyarsk"                
## [285] "Asia/Kuala_Lumpur"                "Asia/Kuching"                    
## [287] "Asia/Kuwait"                      "Asia/Macao"                      
## [289] "Asia/Macau"                       "Asia/Magadan"                    
## [291] "Asia/Makassar"                    "Asia/Manila"                     
## [293] "Asia/Muscat"                      "Asia/Nicosia"                    
## [295] "Asia/Novokuznetsk"                "Asia/Novosibirsk"                
## [297] "Asia/Omsk"                        "Asia/Oral"                       
## [299] "Asia/Phnom_Penh"                  "Asia/Pontianak"                  
## [301] "Asia/Pyongyang"                   "Asia/Qatar"                      
## [303] "Asia/Qostanay"                    "Asia/Qyzylorda"                  
## [305] "Asia/Rangoon"                     "Asia/Riyadh"                     
## [307] "Asia/Saigon"                      "Asia/Sakhalin"                   
## [309] "Asia/Samarkand"                   "Asia/Seoul"                      
## [311] "Asia/Shanghai"                    "Asia/Singapore"                  
## [313] "Asia/Srednekolymsk"               "Asia/Taipei"                     
## [315] "Asia/Tashkent"                    "Asia/Tbilisi"                    
## [317] "Asia/Tehran"                      "Asia/Tel_Aviv"                   
## [319] "Asia/Thimbu"                      "Asia/Thimphu"                    
## [321] "Asia/Tokyo"                       "Asia/Tomsk"                      
## [323] "Asia/Ujung_Pandang"               "Asia/Ulaanbaatar"                
## [325] "Asia/Ulan_Bator"                  "Asia/Urumqi"                     
## [327] "Asia/Ust-Nera"                    "Asia/Vientiane"                  
## [329] "Asia/Vladivostok"                 "Asia/Yakutsk"                    
## [331] "Asia/Yangon"                      "Asia/Yekaterinburg"              
## [333] "Asia/Yerevan"                     "Atlantic/Azores"                 
## [335] "Atlantic/Bermuda"                 "Atlantic/Canary"                 
## [337] "Atlantic/Cape_Verde"              "Atlantic/Faeroe"                 
## [339] "Atlantic/Faroe"                   "Atlantic/Jan_Mayen"              
## [341] "Atlantic/Madeira"                 "Atlantic/Reykjavik"              
## [343] "Atlantic/South_Georgia"           "Atlantic/St_Helena"              
## [345] "Atlantic/Stanley"                 "Australia/ACT"                   
## [347] "Australia/Adelaide"               "Australia/Brisbane"              
## [349] "Australia/Broken_Hill"            "Australia/Canberra"              
## [351] "Australia/Currie"                 "Australia/Darwin"                
## [353] "Australia/Eucla"                  "Australia/Hobart"                
## [355] "Australia/LHI"                    "Australia/Lindeman"              
## [357] "Australia/Lord_Howe"              "Australia/Melbourne"             
## [359] "Australia/North"                  "Australia/NSW"                   
## [361] "Australia/Perth"                  "Australia/Queensland"            
## [363] "Australia/South"                  "Australia/Sydney"                
## [365] "Australia/Tasmania"               "Australia/Victoria"              
## [367] "Australia/West"                   "Australia/Yancowinna"            
## [369] "Brazil/Acre"                      "Brazil/DeNoronha"                
## [371] "Brazil/East"                      "Brazil/West"                     
## [373] "Canada/Atlantic"                  "Canada/Central"                  
## [375] "Canada/Eastern"                   "Canada/Mountain"                 
## [377] "Canada/Newfoundland"              "Canada/Pacific"                  
## [379] "Canada/Saskatchewan"              "Canada/Yukon"                    
## [381] "CET"                              "Chile/Continental"               
## [383] "Chile/EasterIsland"               "CST6CDT"                         
## [385] "Cuba"                             "EET"                             
## [387] "Egypt"                            "Eire"                            
## [389] "EST"                              "EST5EDT"                         
## [391] "Etc/GMT"                          "Etc/GMT-0"                       
## [393] "Etc/GMT-1"                        "Etc/GMT-10"                      
## [395] "Etc/GMT-11"                       "Etc/GMT-12"                      
## [397] "Etc/GMT-13"                       "Etc/GMT-14"                      
## [399] "Etc/GMT-2"                        "Etc/GMT-3"                       
## [401] "Etc/GMT-4"                        "Etc/GMT-5"                       
## [403] "Etc/GMT-6"                        "Etc/GMT-7"                       
## [405] "Etc/GMT-8"                        "Etc/GMT-9"                       
## [407] "Etc/GMT+0"                        "Etc/GMT+1"                       
## [409] "Etc/GMT+10"                       "Etc/GMT+11"                      
## [411] "Etc/GMT+12"                       "Etc/GMT+2"                       
## [413] "Etc/GMT+3"                        "Etc/GMT+4"                       
## [415] "Etc/GMT+5"                        "Etc/GMT+6"                       
## [417] "Etc/GMT+7"                        "Etc/GMT+8"                       
## [419] "Etc/GMT+9"                        "Etc/GMT0"                        
## [421] "Etc/Greenwich"                    "Etc/UCT"                         
## [423] "Etc/Universal"                    "Etc/UTC"                         
## [425] "Etc/Zulu"                         "Europe/Amsterdam"                
## [427] "Europe/Andorra"                   "Europe/Astrakhan"                
## [429] "Europe/Athens"                    "Europe/Belfast"                  
## [431] "Europe/Belgrade"                  "Europe/Berlin"                   
## [433] "Europe/Bratislava"                "Europe/Brussels"                 
## [435] "Europe/Bucharest"                 "Europe/Budapest"                 
## [437] "Europe/Busingen"                  "Europe/Chisinau"                 
## [439] "Europe/Copenhagen"                "Europe/Dublin"                   
## [441] "Europe/Gibraltar"                 "Europe/Guernsey"                 
## [443] "Europe/Helsinki"                  "Europe/Isle_of_Man"              
## [445] "Europe/Istanbul"                  "Europe/Jersey"                   
## [447] "Europe/Kaliningrad"               "Europe/Kiev"                     
## [449] "Europe/Kirov"                     "Europe/Lisbon"                   
## [451] "Europe/Ljubljana"                 "Europe/London"                   
## [453] "Europe/Luxembourg"                "Europe/Madrid"                   
## [455] "Europe/Malta"                     "Europe/Mariehamn"                
## [457] "Europe/Minsk"                     "Europe/Monaco"                   
## [459] "Europe/Moscow"                    "Europe/Nicosia"                  
## [461] "Europe/Oslo"                      "Europe/Paris"                    
## [463] "Europe/Podgorica"                 "Europe/Prague"                   
## [465] "Europe/Riga"                      "Europe/Rome"                     
## [467] "Europe/Samara"                    "Europe/San_Marino"               
## [469] "Europe/Sarajevo"                  "Europe/Saratov"                  
## [471] "Europe/Simferopol"                "Europe/Skopje"                   
## [473] "Europe/Sofia"                     "Europe/Stockholm"                
## [475] "Europe/Tallinn"                   "Europe/Tirane"                   
## [477] "Europe/Tiraspol"                  "Europe/Ulyanovsk"                
## [479] "Europe/Uzhgorod"                  "Europe/Vaduz"                    
## [481] "Europe/Vatican"                   "Europe/Vienna"                   
## [483] "Europe/Vilnius"                   "Europe/Volgograd"                
## [485] "Europe/Warsaw"                    "Europe/Zagreb"                   
## [487] "Europe/Zaporozhye"                "Europe/Zurich"                   
## [489] "GB"                               "GB-Eire"                         
## [491] "GMT"                              "GMT-0"                           
## [493] "GMT+0"                            "GMT0"                            
## [495] "Greenwich"                        "Hongkong"                        
## [497] "HST"                              "Iceland"                         
## [499] "Indian/Antananarivo"              "Indian/Chagos"                   
## [501] "Indian/Christmas"                 "Indian/Cocos"                    
## [503] "Indian/Comoro"                    "Indian/Kerguelen"                
## [505] "Indian/Mahe"                      "Indian/Maldives"                 
## [507] "Indian/Mauritius"                 "Indian/Mayotte"                  
## [509] "Indian/Reunion"                   "Iran"                            
## [511] "Israel"                           "Jamaica"                         
## [513] "Japan"                            "Kwajalein"                       
## [515] "Libya"                            "MET"                             
## [517] "Mexico/BajaNorte"                 "Mexico/BajaSur"                  
## [519] "Mexico/General"                   "MST"                             
## [521] "MST7MDT"                          "Navajo"                          
## [523] "NZ"                               "NZ-CHAT"                         
## [525] "Pacific/Apia"                     "Pacific/Auckland"                
## [527] "Pacific/Bougainville"             "Pacific/Chatham"                 
## [529] "Pacific/Chuuk"                    "Pacific/Easter"                  
## [531] "Pacific/Efate"                    "Pacific/Enderbury"               
## [533] "Pacific/Fakaofo"                  "Pacific/Fiji"                    
## [535] "Pacific/Funafuti"                 "Pacific/Galapagos"               
## [537] "Pacific/Gambier"                  "Pacific/Guadalcanal"             
## [539] "Pacific/Guam"                     "Pacific/Honolulu"                
## [541] "Pacific/Johnston"                 "Pacific/Kiritimati"              
## [543] "Pacific/Kosrae"                   "Pacific/Kwajalein"               
## [545] "Pacific/Majuro"                   "Pacific/Marquesas"               
## [547] "Pacific/Midway"                   "Pacific/Nauru"                   
## [549] "Pacific/Niue"                     "Pacific/Norfolk"                 
## [551] "Pacific/Noumea"                   "Pacific/Pago_Pago"               
## [553] "Pacific/Palau"                    "Pacific/Pitcairn"                
## [555] "Pacific/Pohnpei"                  "Pacific/Ponape"                  
## [557] "Pacific/Port_Moresby"             "Pacific/Rarotonga"               
## [559] "Pacific/Saipan"                   "Pacific/Samoa"                   
## [561] "Pacific/Tahiti"                   "Pacific/Tarawa"                  
## [563] "Pacific/Tongatapu"                "Pacific/Truk"                    
## [565] "Pacific/Wake"                     "Pacific/Wallis"                  
## [567] "Pacific/Yap"                      "Poland"                          
## [569] "Portugal"                         "PRC"                             
## [571] "PST8PDT"                          "ROC"                             
## [573] "ROK"                              "Singapore"                       
## [575] "Turkey"                           "UCT"                             
## [577] "Universal"                        "US/Alaska"                       
## [579] "US/Aleutian"                      "US/Arizona"                      
## [581] "US/Central"                       "US/East-Indiana"                 
## [583] "US/Eastern"                       "US/Hawaii"                       
## [585] "US/Indiana-Starke"                "US/Michigan"                     
## [587] "US/Mountain"                      "US/Pacific"                      
## [589] "US/Pacific-New"                   "US/Samoa"                        
## [591] "UTC"                              "W-SU"                            
## [593] "WET"                              "Zulu"                            
## attr(,"Version")
## [1] "2020a"
```

---

### All time zones

```r
length(OlsonNames())
```

```
## [1] 594
```

```r
OlsonNames()[114:119]
```

```
## [1] "America/Fortaleza"  "America/Glace_Bay"  "America/Godthab"   
## [4] "America/Goose_Bay"  "America/Grand_Turk" "America/Grenada"
```

---

---

```r
today() - ymd("1911/05/31")
```

```
## Time difference of 39974 days
```

```r
since_titanic <- today() - ymd("1911/05/31")
str(since_titanic)
```

```
##  'difftime' num 39974
##  - attr(*, "units")= chr "days"
```

---

## Durations

```r
since_titanic <- as.duration(since_titanic)
str(since_titanic)
```

```
## Formal class 'Duration' [package "lubridate"] with 1 slot
##   ..@ .Data: num 3.45e+09
```

```r
since_titanic
```

```
## [1] "3453753600s (~109.44 years)"
```

---

## Durations

```r
some_date <- ymd("1911/05/31")

some_date + ddays(3)
```

```
## [1] "1911-06-03"
```

```r
some_date + ddays(3) + dseconds(4)
```

```
## [1] "1911-06-03 00:00:04 UTC"
```

---

```r
some_time <- mdy_hms("10/31/2020 10:05:18", 
        tz = "America/Los_Angeles")

some_time
```

```
## [1] "2020-10-31 10:05:18 PDT"
```

```r
some_time + ddays(1)
```

```
## [1] "2020-11-01 09:05:18 PST"
```

Lubridate package takes daylight savings into account.

---

---

## Getting Year

```r
apollo11_return <- ymd_hm("1969/07/21 17:54")
apollo11_return
```

```
## [1] "1969-07-21 17:54:00 UTC"
```

```r
year(apollo11_return)
```

```
## [1] 1969
```

---

## Getting Month

```r
month(apollo11_return)
```

```
## [1] 7
```

```r
month(apollo11_return, label = TRUE)
```

```
## [1] Jul
## 12 Levels: Jan < Feb < Mar < Apr < May < Jun < Jul < Aug < Sep < ... < Dec
```

---

### Getting Day and Day of the Week

```r
day(apollo11_return)
```

```
## [1] 21
```

```r
wday(apollo11_return)
```

```
## [1] 2
```

```r
wday(apollo11_return, label = TRUE)
```

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

---

[lubridate cheatsheet](https://github.com/rstudio/cheatsheets/raw/master/lubridate.pdf)