```r
summarise(group_by(starwars, species), mean(height))
```

```
## # A tibble: 38 x 2
##    species   `mean(height)`
##    <chr>              <dbl>
##  1 Aleena               79 
##  2 Besalisk            198 
##  3 Cerean              198 
##  4 Chagrian            196 
##  5 Clawdite            168 
##  6 Droid                NA 
##  7 Dug                 112 
##  8 Ewok                 88 
##  9 Geonosian           183 
## 10 Gungan              209.
## # ... with 28 more rows
```