使用summarise_all [R]在dplyr组内执行t测试

Question

假设我想用两种不同的货币来比较每个国家的苹果和橘子的价格:美国和BTC。

每个国家的美国水果

各国的BTC ~水果

library(tidyverse)

prices <- tibble(
  country = c(rep("USA", 6), rep("Spain", 6), rep("Korea", 6)),
  fruit = rep(c("apples", "apples", "apples", "oranges", "oranges", "oranges"), 3),
  price_USA = rnorm(18),
  price_BTC = rnorm(18)
)

prices %>% 
  group_by(country) %>% 
  summarise(
    pval_USA = t.test(price_USA ~ fruit)$p.value
    pval_BTC = t.test(price_BTC ~ fruit)$p.value
  )

现在假设有许多列，我希望使用summarise_all而不是命名每个列。是否有一种方法可以在每个组(country)内以及在每个列(price_USA、price_BTC)上使用dplyr::summarise_all函数执行t测试？到目前为止，我尝试过的方法一直给我带来错误。

prices %>% 
  group_by(country) %>% 
  summarise_at(
    c("price_USA", "price_BTC"),
    function(x) {t.test(x ~ .$fruit)$p.value}
  )
> Error in model.frame.default(formula = x ~ .$fruit) : 
  variable lengths differ (found for '.$fruit') 

Answer 1

你可以通过将数据从宽格式转换为长格式来做这件事。下面是使用dplyr的解决方案：

library(tidyverse)

prices <- tibble(
  country = c(rep("USA", 6), rep("Spain", 6), rep("Korea", 6)),
  fruit = rep(c("apples", "apples", "apples", "oranges", "oranges", "oranges"), 3),
  price_USA = rnorm(18),
  price_BTC = rnorm(18)
)

prices %>% 
  pivot_longer(cols = starts_with("price"), names_to = "name",
               values_to = "price", names_prefix = "price_") %>%
  group_by(country, name) %>%
  summarise(pval = t.test(price ~ fruit)$p.value)
#> # A tibble: 6 x 3
#> # Groups:   country [3]
#>   country name   pval
#>   <chr>   <chr> <dbl>
#> 1 Korea   BTC   0.458
#> 2 Korea   USA   0.721
#> 3 Spain   BTC   0.732
#> 4 Spain   USA   0.526
#> 5 USA     BTC   0.916
#> 6 USA     USA   0.679