Extract the first Monday of each month

Question

How can I extract the first Monday of each month from 2010-01-01 to 2015-12-31?

Answer 1

We can use lubridate, wdayto check if this is Monday, and dayto check if this is the first week of the month:

library(lubridate)
x <- seq(ymd("2010-01-01"),ymd("2015-12-31"),by="1 day")
x[wday(x,label = TRUE) == "Mon" & day(x) <= 7]

or in database-r (comment by @DavidArenburg)

x <- seq(as.Date("2010-01-01"), as.Date("2015-12-31"), by = "day")
# You need to adapt "Monday" to the equivalent in your locale
x[weekdays(x) == "Monday" & as.numeric(format(x, "%d")) <= 7]

(five first results)

[1] "2010-01-04 UTC" "2010-02-01 UTC" "2010-03-01 UTC" "2010-04-05 UTC" "2010-05-03 UTC" "2010-06-07 UTC"

Answer 2

Another assessment: using the Boost Date_Time library:

library(RcppBDT)
dates <- seq(as.Date("2010-01-01"), as.Date("2015-12-31"), by="1 month")
do.call(c, lapply(dates-1, getFirstDayOfWeekAfter, dow=Mon))
# [1] "2010-01-04" "2010-02-01" "2010-03-01" "2010-04-05" "2010-05-03"...

Answer 3

Here is the basic solution of R. It only requires three lines of code. In zoo quickref vignette there is one line, nextfrito get the next Friday or after a certain date. If we replace every 5 (Friday) with 1 (Monday) in the body of this function, we get the next Monday or after a certain date. (The formula there does not include the argument originthat is used here, since the zoo allows you to omit it, but here we include it so that it works without any packages.)

# given "Date" class vector x return same date if Mon or next Mon if not
nextmon <- function(x) 7 * ceiling(as.numeric(x-1+4)/7) + as.Date(1-4, origin="1970-01-01")

# all first of months between the indicated dates
firsts <- seq(as.Date("2010-01-01"), as.Date("2015-12-31"), "month")

# first Monday in each month
nextmon(firsts)

`gives:

 [1] "2010-01-04" "2010-02-01" "2010-03-01" "2010-04-05" "2010-05-03"
 [6] "2010-06-07" "2010-07-05" "2010-08-02" "2010-09-06" "2010-10-04"
[11] "2010-11-01" "2010-12-06" "2011-01-03" "2011-02-07" "2011-03-07"
[16] "2011-04-04" "2011-05-02" "2011-06-06" "2011-07-04" "2011-08-01"
[21] "2011-09-05" "2011-10-03" "2011-11-07" "2011-12-05" "2012-01-02"
[26] "2012-02-06" "2012-03-05" "2012-04-02" "2012-05-07" "2012-06-04"
[31] "2012-07-02" "2012-08-06" "2012-09-03" "2012-10-01" "2012-11-05"
[36] "2012-12-03" "2013-01-07" "2013-02-04" "2013-03-04" "2013-04-01"
[41] "2013-05-06" "2013-06-03" "2013-07-01" "2013-08-05" "2013-09-02"
[46] "2013-10-07" "2013-11-04" "2013-12-02" "2014-01-06" "2014-02-03"
[51] "2014-03-03" "2014-04-07" "2014-05-05" "2014-06-02" "2014-07-07"
[56] "2014-08-04" "2014-09-01" "2014-10-06" "2014-11-03" "2014-12-01"
[61] "2015-01-05" "2015-02-02" "2015-03-02" "2015-04-06" "2015-05-04"
[66] "2015-06-01" "2015-07-06" "2015-08-03" "2015-09-07" "2015-10-05"
[71] "2015-11-02" "2015-12-07"