Ensure endpoints() always returns last observation

endpoints() did not return the location of the last observation when
`k > 1` and `on` is "months" or "quarters". This was because the seq()
call did not include the last location.

Create a function to do the check, to keep things DRY.

Thanks to GitHub user Eluvias for the report.

Fixes #300.

R/endpoints.R

@@ -41,6 +41,15 @@ function(x,on='months',k=1) {
   if(on %in% c('years','quarters','months','weeks','days'))
     posixltindex <- as.POSIXlt(.POSIXct(.index(x)),tz=tzone(x))
 
+  include_last <- function(x, k) {
+    len <- length(x)
+    i <- seq(1L ,len, k)
+    if(i[length(i)] != len) {
+      i <- c(i, len)
+    }
+    ep[i]
+  }
+
   switch(on,
     "years" = {
       as.integer(c(0, which(diff(posixltindex$year %/% k + 1) != 0), NR))
@@ -49,16 +58,18 @@ function(x,on='months',k=1) {
       ixyear <- posixltindex$year * 100L + 190000L
       ixqtr <- ixyear + posixltindex$mon %/% 3L + 1L
       ep <- c(0L, which(diff(ixqtr) != 0L), NR)
-      if(k > 1)
-        ep[seq(1,length(ep),k)]
-      else ep
+      if(k > 1) {
+        ep <- include_last(ep, k)
+      }
+      ep
     },
     "months" = {
       ixmon <- posixltindex$year * 100L + 190000L + posixltindex$mon
       ep <- .Call("endpoints", ixmon, 1L, 1L, addlast, PACKAGE='xts')
-      if(k > 1)
-        ep[seq(1,length(ep),k)]
-      else ep
+      if(k > 1) {
+        ep <- include_last(ep, k)
+      }
+      ep
     },
     "weeks" = {
       .Call("endpoints", .index(x)+3L*86400L, 604800L, k, addlast, PACKAGE='xts')

inst/unitTests/runit.endpoints.R

@@ -222,8 +222,46 @@ test.multiple_quarters <- function() {
   x <- xts(1:48, as.yearmon("2015-01-01") + 0:47 / 12)
   checkIdentical(endpoints(x, "quarters", 1), seq(0L, 48L, 3L))
   checkIdentical(endpoints(x, "quarters", 2), seq(0L, 48L, 6L))
-  checkIdentical(endpoints(x, "quarters", 3), seq(0L, 48L, 9L))
+  checkIdentical(endpoints(x, "quarters", 3), c(seq(0L, 48L, 9L), 48L))
   checkIdentical(endpoints(x, "quarters", 4), seq(0L, 48L,12L))
-  checkIdentical(endpoints(x, "quarters", 5), seq(0L, 48L,15L))
-  checkIdentical(endpoints(x, "quarters", 6), seq(0L, 48L,18L))
+  checkIdentical(endpoints(x, "quarters", 5), c(seq(0L, 48L,15L), 48L))
+  checkIdentical(endpoints(x, "quarters", 6), c(seq(0L, 48L,18L), 48L))
+}
+
+# end(x) always in endpoints(x) result
+test.last_obs_always_in_output <- function() {
+  N <- 341*12
+  xx <- xts(rnorm(N), seq(Sys.Date(), by = "day", length.out = N))
+
+  ep <- endpoints(xx, on = "quarters", k = 2) # OK
+  checkIdentical(end(xx), end(xx[ep,]), "quarters, k=2")
+
+  ep <- endpoints(xx, on = "quarters", k = 3) # NOPE
+  checkIdentical(end(xx), end(xx[ep,]), "quarters, k=3")
+
+  ep <- endpoints(xx, on = "quarters", k = 4) # NOPE
+  checkIdentical(end(xx), end(xx[ep,]), "quarters, k=4")
+
+  ep <- endpoints(xx, on = "quarters", k = 5) # NOPE
+  checkIdentical(end(xx), end(xx[ep,]), "quarters, k=5")
+
+  ep <- endpoints(xx, on = "months", k = 2) # NOPE
+  checkIdentical(end(xx), end(xx[ep,]), "months, k=2")
+
+  ep <- endpoints(xx, on = "months", k = 3) # OK
+  checkIdentical(end(xx), end(xx[ep,]), "months, k=3")
+
+  ep <- endpoints(xx, on = "months", k = 4) # NOPE
+  checkIdentical(end(xx), end(xx[ep,]), "months, k=4")
+
+  # For the "weeks" case works fine
+
+  ep <- endpoints(xx, on = "weeks", k = 2) # OK
+  checkIdentical(end(xx), end(xx[ep,]), "weeks, k=2")
+
+  ep <- endpoints(xx, on = "weeks", k = 3) # OK
+  checkIdentical(end(xx), end(xx[ep,]), "weeks, k=3")
+
+  ep <- endpoints(xx, on = "weeks", k = 4) # OK
+  checkIdentical(end(xx), end(xx[ep,]), "weeks, k=4")
 }