Added summarise<fable>() support

NAMESPACE

@@ -142,6 +142,8 @@ S3method(stream,lst_mdl)
 S3method(stream,mdl_df)
 S3method(stream,mdl_ts)
 S3method(stream,null_mdl)
+S3method(summarise,fbl_ts)
+S3method(summarise,grouped_fbl)
 S3method(tidy,mdl_df)
 S3method(tidy,mdl_ts)
 S3method(tidy,null_mdl)

NEWS.md

@@ -7,6 +7,8 @@
   and `generate()`).
 * Improved equality comparison of `agg_vec` classes, aggregated values will now
   always match regardless of the value used.
+* Using `summarise()` with a fable will now retain the fable class if the 
+  distribution still exists under the same variable name.
 * Documentation improvements
 * Performance improvements
 

R/dplyr-fable.R

@@ -24,3 +24,23 @@ dplyr_reconstruct.fbl_ts <- function(data, template) {
 
 #' @export
 dplyr_reconstruct.grouped_fbl <- dplyr_reconstruct.fbl_ts
+
+#' @export
+summarise.fbl_ts <- function(.data, ..., .groups = NULL) { 
+  dist_var <- distribution_var(.data)
+  dist_ptype <- vec_ptype(.data[[dist_var]])
+  resp_var <- response_vars(.data)
+  .data <- summarise(as_tsibble(.data), ..., .groups = .groups)
+
+  # If the distribution is lost, return a tsibble
+  if(dist_var %in% names(.data)) {
+    if(!vec_is(.data[[dist_var]], dist_ptype)){
+      return(.data)
+    }
+  }
+
+  build_fable(.data, response = resp_var, distribution = dist_var)
+}
+
+#' @export
+summarise.grouped_fbl <- summarise.fbl_ts