added hint for cummulative functions (#514)

2017-05-03 09:59:03 -03:00
parent 5e17edb7f1
commit 25b1f7fb1c
1 changed files with 2 additions and 1 deletions
--- a/transform.Rmd
+++ b/transform.Rmd
@@ -832,7 +832,8 @@ daily %>%
    `flights %>% group_by(carrier, dest) %>% summarise(n())`)

 1.  For each plane, count the number of flights before the first delay 
-    of greater than 1 hour.
+    of greater than 1 hour. (Hint: read about cummulative window functions and
+    see how their negations work, `vignette("window-functions")`)

 1.  What does the `sort` argument to `count()` do. When might you use it?