Dates

ISI-BUDS 2025

Working with Dates

library(lubridate)

https://xkcd.com/1179/

today()

[1] "2025-06-26"

now()

[1] "2025-06-26 11:48:27 PDT"

From strings to dates

mdy()

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

str(arrival)

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

mdy(arrival)

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

str(mdy(arrival))

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

mdy("11012005")

[1] "2005-11-01"

mdy("Nov-01-2005")

[1] "2005-11-01"

mdy()

ymd()

dmy()

We can include hours, minutes and seconds too.

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

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

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

These represent date-time vectors in R.

Including time zones

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

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

All time zones

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/Ciudad_Juarez"           
 [97] "America/Coral_Harbour"            "America/Cordoba"                 
 [99] "America/Costa_Rica"               "America/Coyhaique"               
[101] "America/Creston"                  "America/Cuiaba"                  
[103] "America/Curacao"                  "America/Danmarkshavn"            
[105] "America/Dawson"                   "America/Dawson_Creek"            
[107] "America/Denver"                   "America/Detroit"                 
[109] "America/Dominica"                 "America/Edmonton"                
[111] "America/Eirunepe"                 "America/El_Salvador"             
[113] "America/Ensenada"                 "America/Fort_Nelson"             
[115] "America/Fort_Wayne"               "America/Fortaleza"               
[117] "America/Glace_Bay"                "America/Godthab"                 
[119] "America/Goose_Bay"                "America/Grand_Turk"              
[121] "America/Grenada"                  "America/Guadeloupe"              
[123] "America/Guatemala"                "America/Guayaquil"               
[125] "America/Guyana"                   "America/Halifax"                 
[127] "America/Havana"                   "America/Hermosillo"              
[129] "America/Indiana/Indianapolis"     "America/Indiana/Knox"            
[131] "America/Indiana/Marengo"          "America/Indiana/Petersburg"      
[133] "America/Indiana/Tell_City"        "America/Indiana/Vevay"           
[135] "America/Indiana/Vincennes"        "America/Indiana/Winamac"         
[137] "America/Indianapolis"             "America/Inuvik"                  
[139] "America/Iqaluit"                  "America/Jamaica"                 
[141] "America/Jujuy"                    "America/Juneau"                  
[143] "America/Kentucky/Louisville"      "America/Kentucky/Monticello"     
[145] "America/Knox_IN"                  "America/Kralendijk"              
[147] "America/La_Paz"                   "America/Lima"                    
[149] "America/Los_Angeles"              "America/Louisville"              
[151] "America/Lower_Princes"            "America/Maceio"                  
[153] "America/Managua"                  "America/Manaus"                  
[155] "America/Marigot"                  "America/Martinique"              
[157] "America/Matamoros"                "America/Mazatlan"                
[159] "America/Mendoza"                  "America/Menominee"               
[161] "America/Merida"                   "America/Metlakatla"              
[163] "America/Mexico_City"              "America/Miquelon"                
[165] "America/Moncton"                  "America/Monterrey"               
[167] "America/Montevideo"               "America/Montreal"                
[169] "America/Montserrat"               "America/Nassau"                  
[171] "America/New_York"                 "America/Nipigon"                 
[173] "America/Nome"                     "America/Noronha"                 
[175] "America/North_Dakota/Beulah"      "America/North_Dakota/Center"     
[177] "America/North_Dakota/New_Salem"   "America/Nuuk"                    
[179] "America/Ojinaga"                  "America/Panama"                  
[181] "America/Pangnirtung"              "America/Paramaribo"              
[183] "America/Phoenix"                  "America/Port_of_Spain"           
[185] "America/Port-au-Prince"           "America/Porto_Acre"              
[187] "America/Porto_Velho"              "America/Puerto_Rico"             
[189] "America/Punta_Arenas"             "America/Rainy_River"             
[191] "America/Rankin_Inlet"             "America/Recife"                  
[193] "America/Regina"                   "America/Resolute"                
[195] "America/Rio_Branco"               "America/Rosario"                 
[197] "America/Santa_Isabel"             "America/Santarem"                
[199] "America/Santiago"                 "America/Santo_Domingo"           
[201] "America/Sao_Paulo"                "America/Scoresbysund"            
[203] "America/Shiprock"                 "America/Sitka"                   
[205] "America/St_Barthelemy"            "America/St_Johns"                
[207] "America/St_Kitts"                 "America/St_Lucia"                
[209] "America/St_Thomas"                "America/St_Vincent"              
[211] "America/Swift_Current"            "America/Tegucigalpa"             
[213] "America/Thule"                    "America/Thunder_Bay"             
[215] "America/Tijuana"                  "America/Toronto"                 
[217] "America/Tortola"                  "America/Vancouver"               
[219] "America/Virgin"                   "America/Whitehorse"              
[221] "America/Winnipeg"                 "America/Yakutat"                 
[223] "America/Yellowknife"              "Antarctica/Casey"                
[225] "Antarctica/Davis"                 "Antarctica/DumontDUrville"       
[227] "Antarctica/Macquarie"             "Antarctica/Mawson"               
[229] "Antarctica/McMurdo"               "Antarctica/Palmer"               
[231] "Antarctica/Rothera"               "Antarctica/South_Pole"           
[233] "Antarctica/Syowa"                 "Antarctica/Troll"                
[235] "Antarctica/Vostok"                "Arctic/Longyearbyen"             
[237] "Asia/Aden"                        "Asia/Almaty"                     
[239] "Asia/Amman"                       "Asia/Anadyr"                     
[241] "Asia/Aqtau"                       "Asia/Aqtobe"                     
[243] "Asia/Ashgabat"                    "Asia/Ashkhabad"                  
[245] "Asia/Atyrau"                      "Asia/Baghdad"                    
[247] "Asia/Bahrain"                     "Asia/Baku"                       
[249] "Asia/Bangkok"                     "Asia/Barnaul"                    
[251] "Asia/Beirut"                      "Asia/Bishkek"                    
[253] "Asia/Brunei"                      "Asia/Calcutta"                   
[255] "Asia/Chita"                       "Asia/Choibalsan"                 
[257] "Asia/Chongqing"                   "Asia/Chungking"                  
[259] "Asia/Colombo"                     "Asia/Dacca"                      
[261] "Asia/Damascus"                    "Asia/Dhaka"                      
[263] "Asia/Dili"                        "Asia/Dubai"                      
[265] "Asia/Dushanbe"                    "Asia/Famagusta"                  
[267] "Asia/Gaza"                        "Asia/Harbin"                     
[269] "Asia/Hebron"                      "Asia/Ho_Chi_Minh"                
[271] "Asia/Hong_Kong"                   "Asia/Hovd"                       
[273] "Asia/Irkutsk"                     "Asia/Istanbul"                   
[275] "Asia/Jakarta"                     "Asia/Jayapura"                   
[277] "Asia/Jerusalem"                   "Asia/Kabul"                      
[279] "Asia/Kamchatka"                   "Asia/Karachi"                    
[281] "Asia/Kashgar"                     "Asia/Kathmandu"                  
[283] "Asia/Katmandu"                    "Asia/Khandyga"                   
[285] "Asia/Kolkata"                     "Asia/Krasnoyarsk"                
[287] "Asia/Kuala_Lumpur"                "Asia/Kuching"                    
[289] "Asia/Kuwait"                      "Asia/Macao"                      
[291] "Asia/Macau"                       "Asia/Magadan"                    
[293] "Asia/Makassar"                    "Asia/Manila"                     
[295] "Asia/Muscat"                      "Asia/Nicosia"                    
[297] "Asia/Novokuznetsk"                "Asia/Novosibirsk"                
[299] "Asia/Omsk"                        "Asia/Oral"                       
[301] "Asia/Phnom_Penh"                  "Asia/Pontianak"                  
[303] "Asia/Pyongyang"                   "Asia/Qatar"                      
[305] "Asia/Qostanay"                    "Asia/Qyzylorda"                  
[307] "Asia/Rangoon"                     "Asia/Riyadh"                     
[309] "Asia/Saigon"                      "Asia/Sakhalin"                   
[311] "Asia/Samarkand"                   "Asia/Seoul"                      
[313] "Asia/Shanghai"                    "Asia/Singapore"                  
[315] "Asia/Srednekolymsk"               "Asia/Taipei"                     
[317] "Asia/Tashkent"                    "Asia/Tbilisi"                    
[319] "Asia/Tehran"                      "Asia/Tel_Aviv"                   
[321] "Asia/Thimbu"                      "Asia/Thimphu"                    
[323] "Asia/Tokyo"                       "Asia/Tomsk"                      
[325] "Asia/Ujung_Pandang"               "Asia/Ulaanbaatar"                
[327] "Asia/Ulan_Bator"                  "Asia/Urumqi"                     
[329] "Asia/Ust-Nera"                    "Asia/Vientiane"                  
[331] "Asia/Vladivostok"                 "Asia/Yakutsk"                    
[333] "Asia/Yangon"                      "Asia/Yekaterinburg"              
[335] "Asia/Yerevan"                     "Atlantic/Azores"                 
[337] "Atlantic/Bermuda"                 "Atlantic/Canary"                 
[339] "Atlantic/Cape_Verde"              "Atlantic/Faeroe"                 
[341] "Atlantic/Faroe"                   "Atlantic/Jan_Mayen"              
[343] "Atlantic/Madeira"                 "Atlantic/Reykjavik"              
[345] "Atlantic/South_Georgia"           "Atlantic/St_Helena"              
[347] "Atlantic/Stanley"                 "Australia/ACT"                   
[349] "Australia/Adelaide"               "Australia/Brisbane"              
[351] "Australia/Broken_Hill"            "Australia/Canberra"              
[353] "Australia/Currie"                 "Australia/Darwin"                
[355] "Australia/Eucla"                  "Australia/Hobart"                
[357] "Australia/LHI"                    "Australia/Lindeman"              
[359] "Australia/Lord_Howe"              "Australia/Melbourne"             
[361] "Australia/North"                  "Australia/NSW"                   
[363] "Australia/Perth"                  "Australia/Queensland"            
[365] "Australia/South"                  "Australia/Sydney"                
[367] "Australia/Tasmania"               "Australia/Victoria"              
[369] "Australia/West"                   "Australia/Yancowinna"            
[371] "Brazil/Acre"                      "Brazil/DeNoronha"                
[373] "Brazil/East"                      "Brazil/West"                     
[375] "Canada/Atlantic"                  "Canada/Central"                  
[377] "Canada/Eastern"                   "Canada/Mountain"                 
[379] "Canada/Newfoundland"              "Canada/Pacific"                  
[381] "Canada/Saskatchewan"              "Canada/Yukon"                    
[383] "CET"                              "Chile/Continental"               
[385] "Chile/EasterIsland"               "CST6CDT"                         
[387] "Cuba"                             "EET"                             
[389] "Egypt"                            "Eire"                            
[391] "EST"                              "EST5EDT"                         
[393] "Etc/GMT"                          "Etc/GMT-0"                       
[395] "Etc/GMT-1"                        "Etc/GMT-10"                      
[397] "Etc/GMT-11"                       "Etc/GMT-12"                      
[399] "Etc/GMT-13"                       "Etc/GMT-14"                      
[401] "Etc/GMT-2"                        "Etc/GMT-3"                       
[403] "Etc/GMT-4"                        "Etc/GMT-5"                       
[405] "Etc/GMT-6"                        "Etc/GMT-7"                       
[407] "Etc/GMT-8"                        "Etc/GMT-9"                       
[409] "Etc/GMT+0"                        "Etc/GMT+1"                       
[411] "Etc/GMT+10"                       "Etc/GMT+11"                      
[413] "Etc/GMT+12"                       "Etc/GMT+2"                       
[415] "Etc/GMT+3"                        "Etc/GMT+4"                       
[417] "Etc/GMT+5"                        "Etc/GMT+6"                       
[419] "Etc/GMT+7"                        "Etc/GMT+8"                       
[421] "Etc/GMT+9"                        "Etc/GMT0"                        
[423] "Etc/Greenwich"                    "Etc/UCT"                         
[425] "Etc/Universal"                    "Etc/UTC"                         
[427] "Etc/Zulu"                         "Europe/Amsterdam"                
[429] "Europe/Andorra"                   "Europe/Astrakhan"                
[431] "Europe/Athens"                    "Europe/Belfast"                  
[433] "Europe/Belgrade"                  "Europe/Berlin"                   
[435] "Europe/Bratislava"                "Europe/Brussels"                 
[437] "Europe/Bucharest"                 "Europe/Budapest"                 
[439] "Europe/Busingen"                  "Europe/Chisinau"                 
[441] "Europe/Copenhagen"                "Europe/Dublin"                   
[443] "Europe/Gibraltar"                 "Europe/Guernsey"                 
[445] "Europe/Helsinki"                  "Europe/Isle_of_Man"              
[447] "Europe/Istanbul"                  "Europe/Jersey"                   
[449] "Europe/Kaliningrad"               "Europe/Kiev"                     
[451] "Europe/Kirov"                     "Europe/Kyiv"                     
[453] "Europe/Lisbon"                    "Europe/Ljubljana"                
[455] "Europe/London"                    "Europe/Luxembourg"               
[457] "Europe/Madrid"                    "Europe/Malta"                    
[459] "Europe/Mariehamn"                 "Europe/Minsk"                    
[461] "Europe/Monaco"                    "Europe/Moscow"                   
[463] "Europe/Nicosia"                   "Europe/Oslo"                     
[465] "Europe/Paris"                     "Europe/Podgorica"                
[467] "Europe/Prague"                    "Europe/Riga"                     
[469] "Europe/Rome"                      "Europe/Samara"                   
[471] "Europe/San_Marino"                "Europe/Sarajevo"                 
[473] "Europe/Saratov"                   "Europe/Simferopol"               
[475] "Europe/Skopje"                    "Europe/Sofia"                    
[477] "Europe/Stockholm"                 "Europe/Tallinn"                  
[479] "Europe/Tirane"                    "Europe/Tiraspol"                 
[481] "Europe/Ulyanovsk"                 "Europe/Uzhgorod"                 
[483] "Europe/Vaduz"                     "Europe/Vatican"                  
[485] "Europe/Vienna"                    "Europe/Vilnius"                  
[487] "Europe/Volgograd"                 "Europe/Warsaw"                   
[489] "Europe/Zagreb"                    "Europe/Zaporozhye"               
[491] "Europe/Zurich"                    "Factory"                         
[493] "GB"                               "GB-Eire"                         
[495] "GMT"                              "GMT-0"                           
[497] "GMT+0"                            "GMT0"                            
[499] "Greenwich"                        "Hongkong"                        
[501] "HST"                              "Iceland"                         
[503] "Indian/Antananarivo"              "Indian/Chagos"                   
[505] "Indian/Christmas"                 "Indian/Cocos"                    
[507] "Indian/Comoro"                    "Indian/Kerguelen"                
[509] "Indian/Mahe"                      "Indian/Maldives"                 
[511] "Indian/Mauritius"                 "Indian/Mayotte"                  
[513] "Indian/Reunion"                   "Iran"                            
[515] "Israel"                           "Jamaica"                         
[517] "Japan"                            "Kwajalein"                       
[519] "Libya"                            "MET"                             
[521] "Mexico/BajaNorte"                 "Mexico/BajaSur"                  
[523] "Mexico/General"                   "MST"                             
[525] "MST7MDT"                          "Navajo"                          
[527] "NZ"                               "NZ-CHAT"                         
[529] "Pacific/Apia"                     "Pacific/Auckland"                
[531] "Pacific/Bougainville"             "Pacific/Chatham"                 
[533] "Pacific/Chuuk"                    "Pacific/Easter"                  
[535] "Pacific/Efate"                    "Pacific/Enderbury"               
[537] "Pacific/Fakaofo"                  "Pacific/Fiji"                    
[539] "Pacific/Funafuti"                 "Pacific/Galapagos"               
[541] "Pacific/Gambier"                  "Pacific/Guadalcanal"             
[543] "Pacific/Guam"                     "Pacific/Honolulu"                
[545] "Pacific/Johnston"                 "Pacific/Kanton"                  
[547] "Pacific/Kiritimati"               "Pacific/Kosrae"                  
[549] "Pacific/Kwajalein"                "Pacific/Majuro"                  
[551] "Pacific/Marquesas"                "Pacific/Midway"                  
[553] "Pacific/Nauru"                    "Pacific/Niue"                    
[555] "Pacific/Norfolk"                  "Pacific/Noumea"                  
[557] "Pacific/Pago_Pago"                "Pacific/Palau"                   
[559] "Pacific/Pitcairn"                 "Pacific/Pohnpei"                 
[561] "Pacific/Ponape"                   "Pacific/Port_Moresby"            
[563] "Pacific/Rarotonga"                "Pacific/Saipan"                  
[565] "Pacific/Samoa"                    "Pacific/Tahiti"                  
[567] "Pacific/Tarawa"                   "Pacific/Tongatapu"               
[569] "Pacific/Truk"                     "Pacific/Wake"                    
[571] "Pacific/Wallis"                   "Pacific/Yap"                     
[573] "Poland"                           "Portugal"                        
[575] "PRC"                              "PST8PDT"                         
[577] "ROC"                              "ROK"                             
[579] "Singapore"                        "Turkey"                          
[581] "UCT"                              "Universal"                       
[583] "US/Alaska"                        "US/Aleutian"                     
[585] "US/Arizona"                       "US/Central"                      
[587] "US/East-Indiana"                  "US/Eastern"                      
[589] "US/Hawaii"                        "US/Indiana-Starke"               
[591] "US/Michigan"                      "US/Mountain"                     
[593] "US/Pacific"                       "US/Samoa"                        
[595] "UTC"                              "W-SU"                            
[597] "WET"                              "Zulu"                            
attr(,"Version")
[1] "2025b"

All time zones

length(OlsonNames())

[1] 598

OlsonNames()[114:119]

[1] "America/Fort_Nelson" "America/Fort_Wayne"  "America/Fortaleza"  
[4] "America/Glace_Bay"   "America/Godthab"     "America/Goose_Bay"  

Time spans

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

Time difference of 41665 days

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

 'difftime' num 41665
 - attr(*, "units")= chr "days"

Durations

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

Formal class 'Duration' [package "lubridate"] with 1 slot
  ..@ .Data: num 3599856000

since_titanic

[1] "3599856000s (~114.07 years)"

Durations

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

some_date + ddays(3)

[1] "1911-06-03"

some_date + ddays(3) + dseconds(4)

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

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

some_time

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

some_time + ddays(1)

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

Lubridate package takes daylight savings into account.

Components of Date and Time

Getting Year

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

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

year(apollo11_return)

[1] 1969

Getting Month

month(apollo11_return)

[1] 7

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

day(apollo11_return)

[1] 21

wday(apollo11_return)

[1] 2

wday(apollo11_return, label = TRUE)

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

lubridate cheatsheet

Your tasks:

• Download cases/tests/deaths data from CA Open Data Portal.

• Load this new data into R/RStudio using read_csv() function

• What format do dates in both hospitalization and cases/tests/deaths tibbles follow? Let’s make sure that they are of Date type

• Join the two datasets by date and county

• Plot the time series of hospitalization-to-cases ratio in Orange county during 2020-2024 on the days when both metrics are available

ca_covid_hosp <- read_csv("../data/ca_covid_hosp.csv",
                          col_types = cols(
                          todays_date  = col_date("%m/%d/%Y")))

ca_covid_cases <- read_csv("../data/ca_covid_cases.csv",
                          col_types = cols(
                          date  = col_date("%Y-%m-%d")))

ca_covid_cases <- ca_covid_cases |> filter(area_type=="County") |> rename(county=area)

ca_covid_hosp <- ca_covid_hosp |> 
  rename(date=todays_date)

ca_covid_cases_hosp <- full_join(ca_covid_cases, ca_covid_hosp, by = c("date", "county"))