对每个列组合应用函数 [英] Apply a function to each combination of columns

问题描述

我有一个包含 n 列的数据框，我想对每个 组合 列应用一个函数.这与 cor() 函数将数据帧作为输入并生成相关矩阵作为输出的方式非常相似，例如:

I have a data frame with n columns and want to apply a function to each combination of columns. This is very similar to how the cor() function takes a data frame as input and produces a correlation matrix as output, for example:

X <- data.frame(A=rnorm(100), B=rnorm(100), C=rnorm(100))
cor(X)

哪个将生成此输出:

> cor(X)
            A           B          C
A  1.00000000 -0.01199511 0.02337429
B -0.01199511  1.00000000 0.07918920
C  0.02337429  0.07918920 1.00000000

但是，我有一个自定义函数，需要将其应用于每个列组合.我现在正在使用使用嵌套 for 循环的解决方案，该解决方案有效:

However, I have a custom function that I need to apply to each combination of columns. I am now using a solution that uses nested for loops, which works:

f <- function(x, y) sum((x+y)^2) # some placeholder function

out <- matrix(NA, ncol = ncol(X), nrow = ncol(X)) # pre-allocate
for(i in seq_along(X)) {
  for(j in seq_along(X)) {
    out[i, j] <- f(X[, i], X[, j]) # apply f() to each combination
  }
}

产生:

> out
         [,1]     [,2]     [,3]
[1,] 422.4447 207.0833 211.4198
[2,] 207.0833 409.1242 218.2430
[3,] 211.4198 218.2430 397.5321

<小时>

我目前正在尝试过渡到 tidyverse，并且希望避免使用 for 循环.有人可以向我展示针对这种情况的整洁解决方案吗?谢谢！

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I am currently trying to transition into the tidyverse and would prefer to avoid using for loops. Could someone show me a tidy solution for this situation? Thanks!

推荐答案

You can do

library(tidyverse)
f <- function(x, y) sum((x+y)^2)
X <- data.frame(A=rnorm(100), B=rnorm(100), C=rnorm(100))

as.list(X) %>%
  expand.grid(., .) %>%
  mutate(out = map2_dbl(Var1, Var2, f)) %>%
  as_tibble()

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