使用 gsub() 从每行多个项目的列表中提取唯一数字？

Question

列表 A1 的结构如下：

#[[1]] [1] "12" "1"

#[[2]] [1] "13" "1"

#[[3]] [1] "14" "2"

#[[4]] [1] "15" "2"

#[[5]] [1] "16" "1"

#[[6]] [1] "18" "2"

#[[7]] [1] "20" "0"

#[[8]] [1] "21" "2"

#[[9]] [1] "21" "4"

#[[10]] [1] "34" "1" "0"

#[[11]] [1] "42" "1" "1"

#[[12]] [1] "42" "2" "2"

并且我正在尝试提取每个列表元素的第一项中的唯一值（例如，[[1]] 中的数字 12）。

当我使用 v <- unique(gsub( " .*$", "", A1))

生成的向量 v 看起来像

"c("12"," "c("13"," "c("14"," "c("15"," "c("16"," "c("18"," "c("20"," "c("21"," "c("34"," "c("42","

期望的结果是 (12, 13, 14, 15, 16, 17, 18, 20, 21, 34, 42)

如何去掉额外的字符，它们从哪里来？

提前致谢！

Answer 1

您可以使用

v <- list(c("12", "1"), c("13", "1"), c("12", "3"))
unique(sapply(v, "[[", 1))
# => [1] "12" "13"

注:

Extract unique numbers from a list with multiple items per line using gsub()?