Is there a package or function in R that lets you easily get the day of the week from the dates?
datas <- c("2010-06-28", "2011-05-25", "2010-09-28", "2011-12-05", "2010-09-14",
"2010-01-01", "2010-01-02", "2010-01-03", "2010-01-04", "2010-01-04",
"2010-01-04", "2010-01-05", "2010-01-05", "2010-01-05", "2010-01-07",
)
To format dates in general you can use the format() function. The functions weekdays() and months() , for example, in the background are wrappers for format() .
To extract the day of the week you will ask for %a or %A , depending on whether you want the abbreviated day of the week or not:
datas <- c("2010-06-28", "2011-05-25", "2010-09-28", "2011-12-05", "2010-09-14",
"2010-01-01", "2010-01-02", "2010-01-03", "2010-01-04", "2010-01-04",
"2010-01-04", "2010-01-05", "2010-01-05", "2010-01-05", "2010-01-07")
format.Date(as.Date(datas), "%a") # abreviado
[1] "seg" "qua" "ter" "seg" "ter" "sex" "sáb" "dom" "seg" "seg" "seg" "ter" "ter" "ter" "qui"
format.Date(as.Date(datas), "%A")
[1] "segunda-feira" "quarta-feira" "terça-feira" "segunda-feira" "terça-feira"
[6] "sexta-feira" "sábado" "domingo" "segunda-feira" "segunda-feira"
[11] "segunda-feira" "terça-feira" "terça-feira" "terça-feira" "quinta-feira"
The two functions are equivalent to:
weekdays(as.Date(datas), abbreviate = TRUE)
weekdays(as.Date(datas))
I put the format because if you want to get more things beyond the day of the week is easier. For example:
format.Date(as.Date(datas), "%a, %d de %B de %Y")
[1] "seg, 28 de junho de 2010" "qua, 25 de maio de 2011" "ter, 28 de setembro de 2010"
[4] "seg, 05 de dezembro de 2011" "ter, 14 de setembro de 2010" "sex, 01 de janeiro de 2010"
[7] "sáb, 02 de janeiro de 2010" "dom, 03 de janeiro de 2010" "seg, 04 de janeiro de 2010"
[10] "seg, 04 de janeiro de 2010" "seg, 04 de janeiro de 2010" "ter, 05 de janeiro de 2010"
[13] "ter, 05 de janeiro de 2010" "ter, 05 de janeiro de 2010" "qui, 07 de janeiro de 2010"
df = data.frame(date=c("2012-02-01", "2012-02-01", "2012-02-02"))
df$day <- weekdays(as.Date(df$date))
df
## data dia
## 1 2012-02-01 Quarta
## 2 2012-02-01 Quarta
## 3 2012-02-02 Quinta