#数据框
> df <- data.frame(id=c(1,2,3,4),name=c("a","b","c","d"),gender=c(TRUE,TRUE,FALSE,FALSE))
> nrow(df) #4行
[1] 4
> ncol(df) #3列
[1] 3
> df2 <- data.frame(id=c(1,2,3,4),score=c(80,86,90,100))
> df2
id score
1 1 80
2 2 86
3 3 90
4 4 100
> data.matrix(df2)
id score
[1,] 1 80
[2,] 2 86
[3,] 3 90
[4,] 4 100