Merge pull request #8 from murraycadzow/patch-1

fix anti vs semi join filter equivalents

Author: MattBixley

docs/2.relational_data.md

@@ -133,10 +133,10 @@ These are similar to piping a data frame to a `filter()`:
 
     ```r
     # anti_join(x, y)
-    filter(x, key %in% y$key)
+    filter(x, !(key %in% y$key))
 
     # semi_join(x, y)
-    filter(x, !(key %in% y$key))
+    filter(x, key %in% y$key)
     ```
 
 Personally, I prefer using `filter()` for its flexibility and verbose syntax, and then perform joining operations when necessary.