More about join diagrams

relational-data.Rmd

@@ -163,6 +163,13 @@ knitr::include_graphics("diagrams/join-setup2.png")
 
 (If you look closely, you might notice that we've switched the order of the keys and values in `x`. This is to emphasise that joins match based on the key variable; value variable is just carried along for the ride.)
 
+In an actual join, matches will be indicated with dots. The colour of the dots match the colour of the keys to remind that that's what important. Then the number of dots = the number of matches = the number of rows in the output.
+
+```{r, echo = FALSE, out.width = "70%"}
+knitr::include_graphics("diagrams/join-inner.png")
+```
+
+
 ### Inner join {#inner-join}
 
 The simplest type of join is the __inner join__. An inner join matches pairs of observations whenever their keys are equal: