r语言 - 将命名向量中的元素按字符模式分组，并找出每组的最大值

Question

假设我有以下向量

test <- c("x1" = 0.1, "x2" = 0.3, "x3" = 0.4,
"y1" = 0.1, "y2" = 0.5, "y3" = 0.4,
"z1" = 0.5, "z2" = 0.3, "z3" = 0.4)
test
#  x1  x2  x3  y1  y2  y3  z1  z2  z3 
# 0.1 0.3 0.4 0.1 0.5 0.4 0.5 0.3 0.4

我想找到值最高的向量元素，按字母分组。在这种情况下，我希望输出是"x3"， "y2"， "z1"。棘手的是，我事先不知道有多少个不同的字母组，也不知道每个字母有多少个数字。因此，我需要一个简单而灵活的代码，它不需要预先指定的分组。

对于使用哪些函数有什么建议吗?

Answer 1

我的解决方案是详细介绍。

## can also use `grp <- stringr::str_remove(names(test), "[0-9]+")`
grp <- stringr::str_extract(names(test), "[A-Za-z]+")
#[1] "x" "x" "x" "y" "y" "y" "z" "z" "z"
## split vector by group
lst <- unname(split(test, grp))
#[[1]]
# x1  x2  x3 
#0.1 0.3 0.4 
#
#[[2]]
# y1  y2  y3 
#0.1 0.5 0.4
#
#[[3]]
# z1  z2  z3 
#0.5 0.3 0.4 
## since you want to keep the names "x3", "y2", "z1"
## it is not satisfactory to simply do `sapply(lst, max)`
sapply(lst, function (x) x[which.max(x)])
# x3  y2  z1 
#0.4 0.5 0.5 

代码足够健壮，可以处理以下更复杂的情况。

hard <- c("x3" = 0.1, "x2" = 0.3, "x1" = 0.4,
"Yy1" = 0.1, "Yy2" = 0.5, "Yy3" = 0.4,
"z0" = 0.5, "z1" = 0.3, "z2" = 0.4)
# x3  x2  x1 Yy1 Yy2 Yy3  z0  z1  z2 
#0.1 0.3 0.4 0.1 0.5 0.4 0.5 0.3 0.4
grp <- stringr::str_extract(names(hard), "[A-Za-z]+")
lst <- unname(split(hard, grp))
sapply(lst, function (x) x[which.max(x)])
# x1 Yy2  z0 
#0.4 0.5 0.5