clean up c.stars() for time sequences

closes #703

NEWS.md

@@ -1,5 +1,7 @@
 # version 0.6-8
 
+* `c.stars()` is more strict when combining time sequences; #703
+
 * fix plotting when breaks contain duplicates; #728
 
 * fix `st_as_stars.im()`; #727 and #648, thanks to Barry Rowlingson

R/dimensions.R

@@ -792,9 +792,11 @@ as.POSIXct.stars = function(x, ...) {
 	d = st_dimensions(x)
 	e = expand_dimensions(d)
 	for (i in seq_along(d)) {
-		p = try(as.POSIXct(e[[i]]), silent = TRUE)
-		if (!inherits(p, "try-error"))
-			d[[i]] = create_dimension(values = p)
+		if (inherits(e[[i]], c("Date", "POSIXt", "udunits", "PCICt"))) {
+			p = try(as.POSIXct(e[[i]]), silent = TRUE)
+			if (!inherits(p, "try-error"))
+				d[[i]] = create_dimension(values = p)
+		}
 	}
 	structure(x, dimensions = d)
 }

R/stars.R

@@ -904,13 +904,20 @@ merge.stars = function(x, y, ..., name = "attributes") {
 }
 
 sort_out_along = function(ret) { 
-	d1 = st_dimensions(ret[[1]])
-	d2 = st_dimensions(ret[[2]])
-	if ("time" %in% names(d1) && (isTRUE(d1$time$offset != d2$time$offset) || 
-			!any(d1$time$values %in% d2$time$values)))
-		"time"
-	else
-		NA_integer_
+	# https://github.com/r-spatial/stars/issues/703 :
+	# 1. check that time is a dimension name in all objects 
+	l = lapply(ret, st_dimensions)
+	if (!all(sapply(l, function(x) "time" %in% names(x))))
+		return(NA_integer_)
+	# 2. check that time values do not overlap
+	lv = lapply(l, st_get_dimension_values, "time")
+	for (i in seq_along(lv)) {
+		if (!inherits(lv[[i]], c("POSIXt", "Date", "PCICt")))
+			return(NA_integer_)
+		if (i < length(lv) && max(lv[[i]]) >= min(lv[[i+1]])) # no sequence
+			return(NA_integer_)
+	}
+	return("time")
 }