Rdatatable · LunaticSage218 · Apr 23, 2026
@@ -388,6 +388,8 @@ See [#2611](https://github.com/Rdatatable/data.table/issues/2611) for details. T
 
 20. `fread()` now supports the `comment.char` argument to skip trailing comments or comment-only lines, consistent with `read.table()`, [#856](https://github.com/Rdatatable/data.table/issues/856). The default remains `comment.char = ""` (no comment parsing) for backward compatibility and performance, in contrast to `read.table(comment.char = "#")`. Thanks to @arunsrinivasan and many others for the suggestion and @ben-schwen for the implementation.
 
+21. `yearqtr()` and `yearmon()` now gain an optional format specifier [#7694](https://github.com/Rdatatable/data.table/issues/7694). 'numeric' is the deafult, which preserves the original behavior, but 'character' formats `yearqtr()` as YYYYQ# (e.g. 2025Q2) and `yearmon()` as YYYYM## (e.g. 2025M02, 2025M10). Thanks to @jan-swissre for the report and @LunaticSage218 for the implementation. 
+
 ### BUG FIXES
 
 1. `fread()` no longer warns on certain systems on R 4.5.0+ where the file owner can't be resolved, [#6918](https://github.com/Rdatatable/data.table/issues/6918). Thanks @ProfFancyPants for the report and PR.

@@ -365,8 +365,30 @@ isoyear = function(x) as.integer(format(as.IDate(x), "%G"))
 month   = function(x) convertDate(as.IDate(x), "month")
 quarter = function(x) convertDate(as.IDate(x), "quarter")
 year    = function(x) convertDate(as.IDate(x), "year")
-yearmon = function(x) convertDate(as.IDate(x), "yearmon")
-yearqtr = function(x) convertDate(as.IDate(x), "yearqtr")
+yearmon = function(x, format=c("numeric", "character")) {
+  format = match.arg(format)
+  x_as_idate = as.IDate(x)
+  ymon = convertDate(x_as_idate, "yearmon")
+  if (format == "numeric") return(ymon)
+  ans = rep(NA_character_, length(x_as_idate))
+  ok = !is.na(x_as_idate)
+  yr = floor(ymon[ok])
+  mon = round((ymon[ok] - yr) * 12) + 1L
+  ans[ok] = sprintf("%dM%02d", as.integer(yr), as.integer(mon))
+  ans
+}
+yearqtr = function(x, format=c("numeric", "character")) {
+  format = match.arg(format)
+  x_as_idate = as.IDate(x)
+  yqtr = convertDate(x_as_idate, "yearqtr")
+  if (format == "numeric") return(yqtr)
+  ans = rep(NA_character_, length(x_as_idate))
+  ok = !is.na(x_as_idate)
+  yr = floor(yqtr[ok])
+  qtr = round((yqtr[ok] - yr) * 4) + 1L
+  ans[ok] = paste0(yr, "Q", qtr)
+  ans
+}
 
 convertDate = function(x, type) {
   type = match.arg(type, c("yday", "wday", "mday", "week", "month", "quarter", "year", "yearmon", "yearqtr"))

@@ -21591,3 +21591,17 @@ x = fread("x\n-1-01-01")$x
 test(2368.1, year(x), -1L)
 test(2368.2, month(x), 1L)
 test(2368.3, mday(x),  1L)
+
+# yearqtr() and yearmon() could optionally output 2025Q4 format #7694
+x = c("1111-11-11", "2019-01-01", "2019-02-28", "2019-03-01", "2019-12-31", "2020-02-29", "2020-03-01", "2020-12-31", "2040-01-01", "2040-12-31", "2100-03-01", NA)
+test(2369.1, yearqtr(x, format="numeric"), c(1111.75, 2019, 2019, 2019, 2019.75, 2020, 2020, 2020.75, 2040, 2040.75, 2100, NA))
+test(2369.2, yearqtr(x, format="numeric"), yearqtr(x))  # numeric is the default, preserves backwards compatibility
+test(2369.3, yearqtr(x, format="character"), c("1111Q4", "2019Q1", "2019Q1", "2019Q1", "2019Q4", "2020Q1", "2020Q1", "2020Q4", "2040Q1", "2040Q4", "2100Q1", NA_character_))
+test(2369.4, yearqtr("2016-08-03 01:02:03.45", format="character"), "2016Q3")
+test(2369.5, yearqtr(NA, format="character"), NA_character_)
+
+test(2370.1, yearmon(x, format="numeric"), c(1111+10/12, 2019, 2019+1/12, 2019+2/12, 2019+11/12, 2020+1/12, 2020+2/12, 2020+11/12, 2040, 2040+11/12, 2100+2/12, NA))
+test(2370.2, yearmon(x, format="numeric"), yearmon(x))  # numeric is the default, preserves backwards compatibility
+test(2370.3, yearmon(x, format="character"), c("1111M11", "2019M01", "2019M02", "2019M03", "2019M12", "2020M02", "2020M03", "2020M12", "2040M01", "2040M12", "2100M03", NA_character_))
+test(2370.4, yearmon("2016-08-03 01:02:03.45", format="character"), "2016M08")
+test(2370.5, yearmon(NA, format="character"), NA_character_)
@@ -97,8 +97,8 @@ isoyear(x)
 month(x)
 quarter(x)
 year(x)
-yearmon(x)
-yearqtr(x)
+yearmon(x, format = c("numeric", "character"))
+yearqtr(x, format = c("numeric", "character"))
 
 }
 
@@ -115,6 +115,7 @@ yearqtr(x)
   the S3 generic.}
   \item{units}{one of the units listed for truncating. May be abbreviated.}
   \item{ms}{ For \code{as.ITime} methods, what should be done with sub-second fractions of input? Valid values are \code{'truncate'} (floor), \code{'nearest'} (round), and \code{'ceil'} (ceiling). See Details. }
+  \item{format}{For \code{yearmon} and \code{yearqtr}, either \code{"numeric"} (default) or \code{"character"}. \code{"character"} formats the result as \code{"2025M04"} for \code{yearmon} and \code{"2025Q2"} for \code{yearqtr}.}
 }
 \details{
 \code{IDate} is a date class derived from \code{Date}. It has the same
@@ -209,7 +210,11 @@ Similarly, \code{isoyear()} returns the ISO 8601 year corresponding to the ISO w
    for second, minute, hour, day of year, day of week,
    day of month, week, month, quarter, and year, respectively.
    \code{yearmon} and \code{yearqtr} return double values representing
-   respectively \code{year + (month-1) / 12} and \code{year + (quarter-1) / 4}.
+   respectively \code{year + (month-1) / 12} and \code{year + (quarter-1) / 4}
+   when \code{format = "numeric"} (the default). When \code{format = "character"},
+   they return character vectors of the form \code{"YYYYMMM"} (e.g. \code{"2025M04"},
+   zero-padded for sortability) and \code{"YYYYQN"} (e.g. \code{"2025Q2"}) respectively,
+   with \code{NA} input returned as \code{NA_character_}.
 
    \code{second}, \code{minute}, \code{hour} are taken directly from
    the \code{POSIXlt} representation.
@@ -296,6 +301,11 @@ year(d2)
 isoweek(d2)
 isoyear(d2)
 
+# Character format for yearmon() and yearqtr()
+d3 = as.IDate(c("2019-01-01", "2019-12-31"))
+yearmon(d3, format = "character") # "2019M01" "2019M12"
+yearqtr(d3, format = "character") # "2019Q1"  "2019Q4"
+
 }
 \keyword{utilities}