如何从存储数据框行的列表中提取行号并写入vector

我有一个由单个行DataFrame组成的列表，定义如下：

kl <- list(structure(list(GROUP = "1", col6 = NA_character_, col7 = NA_character_, 
    dif = NA_character_, p.value = NA_character_), row.names = 1L, class = "data.frame"), 
    structure(list(GROUP = "2", col6 = NA_character_, col7 = NA_character_, 
        dif = NA_character_, p.value = NA_character_), row.names = 3L, class = "data.frame"), 
    structure(list(GROUP = "3", col6 = NA_character_, col7 = NA_character_, 
        dif = NA_character_, p.value = NA_character_), row.names = 5L, class = "data.frame"), 
    structure(list(GROUP = "4", col6 = NA_character_, col7 = NA_character_, 
        dif = NA_character_, p.value = NA_character_), row.names = 7L, class = "data.frame"))

需要提取每个DataFrame的行号，生成包含1,3,5,7的整数向量。

实现方案 #

基础R方法

利用sapply遍历列表，提取每个元素的行名并转换为整数：

kl.vec <- sapply(kl, function(df) as.integer(row.names(df)))

tidyverse方法（使用purrr）

如果使用tidyverse工具集，map_int可以更直观地完成整数向量的生成：

library(purrr)
kl.vec <- map_int(kl, ~ as.integer(row.names(.x)))

两种方法执行后，kl.vec都会得到c(1, 3, 5, 7)的结果。

内容的提问来源于stack exchange，提问作者GOGA GOGA