R语言——分组求值

求iris数据集中的三个物种的Sepal.Length属性的平均值：

1. aggregate

> aggregate(Sepal.Length~Species,data = iris,mean)
     Species Sepal.Length
1     setosa        5.006
2 versicolor        5.936
3  virginica        6.588

2. group_by

> library(tidyverse)
> iris %>% 
+   group_by(Species) %>%
+   summarize(mean(Sepal.Length))
`summarise()` ungrouping output (override with `.groups` argument)
# A tibble: 3 x 2
  Species    `mean(Sepal.Length)`
                       
1 setosa                     5.01
2 versicolor                 5.94
3 virginica                  6.59