Vignette Title

library(MASS)
dat <- MASS::birthwt

birthwt$race <- c("White", "Black", "Other")[birthwt$race]##取得birthwt資料框中race的欄位
aggregate(bwt ~ race, length, data = dat)

##   race bwt
## 1    1  96
## 2    2  26
## 3    3  67

race 1=White 2=Black 3=Other