Honor k > 1 when on = "quarters"

endpoints() completely ignored the 'k' argument when on = "quarters".
Use the same logic for k > 1 when on = "months": calculate endpoints
for k = 1, then subset the result from 1 to length(endpoints) by k.

Fixes #279.

NEWS

@@ -1,3 +1,8 @@
+Changed in xts 0.11-2.1:
+
+o  endpoints() now honors k > 0 when on = "quarters". Thanks to @alkment for
+   the report (#279).
+
 Changed in xts 0.11-2:
 
 o  The to.period() family of functions now use the index timezone when

R/endpoints.R

@@ -46,8 +46,12 @@ function(x,on='months',k=1) {
       as.integer(c(0, which(diff(posixltindex$year %/% k + 1) != 0), NR))
     },
     "quarters" = {
-      ixqtr <- posixltindex$year * 100L + 190000L + posixltindex$mon %/% 3 + 1
-      as.integer(c(0,which(diff(ixqtr) != 0),NR))
+      ixyear <- posixltindex$year * 100L + 190000L
+      ixqtr <- ixyear + posixltindex$mon %/% 3L + 1L
+      ep <- c(0L, which(diff(ixqtr) != 0L), NR)
+      if(k > 1)
+        ep[seq(1,length(ep),k)]
+      else ep
     },
     "months" = {
       ixmon <- posixltindex$year * 100L + 190000L + posixltindex$mon

inst/unitTests/runit.endpoints.R

@@ -216,3 +216,14 @@ test.sub_second_resolution_representation <- function() {
   ep <- endpoints(x, "ms", 200)
   checkIdentical(ep, seq(0L, 10L, 2L))
 }
+
+# on = "quarters", k > 1
+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", 4), seq(0L, 48L,12L))
+  checkIdentical(endpoints(x, "quarters", 5), seq(0L, 48L,15L))
+  checkIdentical(endpoints(x, "quarters", 6), seq(0L, 48L,18L))
+}