我有一个距离函数，它接收2个（数字）向量并计算它们之间的距离。
对于下面示例中的给定数据帧（mtcars_raw）和固定输入向量（test_vec），我想计算每列的成对距离（即应用距离函数）{ {1}}并返回距离矢量。向量的长度应该是列数。
请参阅可重复的示例：
test_vec有人可以显示library(datasets)
# The raw dataframe containing only numeric columns
mtcars_raw <- datasets::mtcars
# The distance function between 2 vectors (of the same length typically)
eucl_dist <- function(x, y){
return(sqrt(sum((x-y)^2)))
}
# An example of a numeric vector to check the distance against each column
test_vec <- rnorm(n = dim(mtcars_raw)[1], mean = 12, sd = 2)
# Manually for the first column, we would have:
dist_1 <- eucl_dist(x = test_vec, mtcars_raw[, 1])
dist_1
#> [1] 58.71256
# Manually for the second column, we would have:
dist_2 <- eucl_dist(x = test_vec, mtcars_raw[, 1])
dist_2
#> [1] 58.71256
# Would like dist_comb returned for all columns without having to manually do
# the combining
dist_comb <- c(dist_1, dist_2)
dist_comb
#> [1] 58.71256 58.71256
代码，在mtcars_raw的每一列上针对test_vec返回向量吗？
答案 0 :(得分：1)
使用map_dbl，map的特殊情况循环遍历列，但显式返回双类型向量：
map_dbl(mtcars_raw[1:2], ~ eucl_dist(test_vec, .x))
# mpg cyl
#58.06386 36.51686
在所有列上：
map_dbl(mtcars_raw, ~ eucl_dist(test_vec, .x))
# mpg cyl disp hp drat wt qsec vs am gear carb
# 58.06386 36.51686 1414.98943 850.71261 49.72837 51.74005 35.50658 67.25079 67.35504 49.34896 54.56577