Converting Date to a Day of Week in R

Date to Day conversion R

You could use the format function with %a or %A

date <- as.Date("2017-05-20")
format(date, "%A")
[1] "Saturday"
format(date, "%a")
[1] "Sat"

If your original date is in the format "07/29/05" in the column A$Date you can call

strDays <- format(as.Date(A$Date, "%m/%d/%y"), "%A")

Find the day of a week

df = data.frame(date=c("2012-02-01", "2012-02-01", "2012-02-02")) 
df$day <- weekdays(as.Date(df$date))
df
##         date       day
## 1 2012-02-01 Wednesday
## 2 2012-02-01 Wednesday
## 3 2012-02-02  Thursday

Edit: Just to show another way...

The wday component of a POSIXlt object is the numeric weekday (0-6 starting on Sunday).

as.POSIXlt(df$date)$wday
## [1] 3 3 4

which you could use to subset a character vector of weekday names

c("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", 
    "Friday", "Saturday")[as.POSIXlt(df$date)$wday + 1]
## [1] "Wednesday" "Wednesday" "Thursday" 

Convert day of week number to weekday name in R

Simple way with dplyr.

library(dplyr)

df <- data.frame(day_number=0:6)

df$day_number <- recode(df$day_number, 
       "0"="Sunday",
       "1"="Monday",
       "2"="Tuesday",
       "3"="Wednesday",
       "4"="Thursday",
       "5"="Friday",
       "6"="Saturday")

Convert a date to a day number (monday = 1, tuesday = 2) in R

You can do this easily with lubridate although it indexes Sunday as '1'. So since March 1, 2014 was a Saturday it would return '7'

library(lubridate)
wday(mdy("3-1-2014"))
[1] 7

Converting date with time in a column to week in character in R

We can floor the Date object with floor_date and then use format

library(dplyr)
library(lubridate)
df1 %>% 
    mutate(Time = as.POSIXct(Time), 
           favorite_time =   format(floor_date(Time, "weeks",
                 week_start = 1), "%B %dth, %Y"))
#  Case                Time      favorite_time
#1    1 2020-01-12 11:28:46 January 06th, 2020
#2    2 2020-01-22 10:17:24 January 20th, 2020

data

df1 <- structure(list(Case = 1:2, Time = c("2020-01-12 11:28:46", 
"2020-01-22 10:17:24"
)), class = "data.frame", row.names = c(NA, -2L))

R function to take a date and output the day of the week for that date?

You can use the format function:

format(as.Date("5/20/2020", '%m/%d/%Y'), "%a")
#[1] "Wed"

format(as.Date("5/20/2020", '%m/%d/%Y'), "%A")
[1] "Wednesday"

All the formats can be seen in the help page of strptime.

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