R purrr keep_at 根據元素的名稱/位置保留/丟棄元素

keep_at(x, at)

discard_at(x, at)

keep() /discard() 按值保留/丟棄元素。

x <- c(a = 1, b = 2, cat = 10, dog = 15, elephant = 5, e = 10)
x %>% keep_at(letters)
#>  a  b  e 
#>  1  2 10 
x %>% discard_at(letters)
#>      cat      dog elephant 
#>       10       15        5 

# Can also use a function
x %>% keep_at(~ nchar(.x) == 3)
#> cat dog 
#>  10  15 
x %>% discard_at(~ nchar(.x) == 3)
#>        a        b elephant        e 
#>        1        2        5       10