計算滿足 R 中多個條件的行數

Question

我有一個數據框：

df <- data.frame (ID  = c(1:20),
                  Ethnicity = c(rep(c("White", "Asian", "Black", "Hispanic", "Other"), times=20/5)),
                  Age = c(1:20),
                  Set = rep(c(1,2,3,4), times=20/4)
)

計算Ethnicity == 'Asian' 和Set == 3 的行數的最有效方法是什么？

謝謝！

Answer 1

取決於您對效率的衡量標准，但是

sum(df$Ethnicity== 'Asian' & df$Set == 3)