1. 当函数有多个返回值的时候，打包成一个list

2. 对矩阵的行列进行命名的时候

matrix(1:9, nrow = 3, byrow = TRUE,
             dimnames = list(c("r1","r2","r3"), c("c1","c2","c3")))

3. as.list

as.list() # 将向量转换成列表：
l2 = as.list(c(a = 1, b = 2))
l2
#> $a
#> [1] 1
#>
#> $b
#> [1] 2

4.对满足条件的列做多种汇总

df_grp = df %>%
group_by(class) %>%
summarise(across(where(is.numeric),list(sum=sum, mean=mean, min=min), na.rm = TRUE))

~~ df ~~