r - 如何在 R 中的不同大小的列中找到公共(public)元素？

Question

我有一个名为 animals 的数据框，其中包含不同大小的列，这些列之间有一些常见和不常见的元素，如下所示:

Dog     Cat      Lion     Dog
Cat     Lion     Dog      Shark
Lion    Dog      Shark    Cat
Shark   Shark    Cat      Lion
        Whale    Seal     Moose
        Seal              Whale
                          Deer

我想要做的是识别每一列中的所有公共(public)元素，排除不常见的元素并将公共(public)元素组合到一列中，如下所示:

Dog
Cat
Lion
Shark

到目前为止，我已经尝试使用 duplicated(animals) 识别重复的元素，然后使用 animals[duplicated(animals)] 提取重复的元素，但这没有给出结果。谁有更好的方法？

Answer 1

我们可以使用intersect

Reduce(intersect, animals)
#[1] "Dog"   "Cat"   "Lion"  "Shark"

---

或者可以使用tidyverse

library(dplyr)
library(tidyr)
pivot_longer(animals, cols = everything(), values_drop_na = TRUE) %>% 
     group_by(value) %>% 
     filter(n_distinct(name) == ncol(animals)) %>% 
     ungroup %>% 
     distinct(value)
# A tibble: 4 x 1
#  value
#  <chr>
#1 Dog  
#2 Cat  
#3 Lion 
#4 Shark

数据

animals <- structure(list(v1 = c("Dog", "Cat", "Lion", "Shark", NA, NA, 
NA), v2 = c("Cat", "Lion", "Dog", "Shark", "Whale", "Seal", NA
), v3 = c("Lion", "Dog", "Shark", "Cat", "Seal", NA, NA), v4 = c("Dog", 
"Shark", "Cat", "Lion", "Moose", "Whale", "Deer")), 
    class = "data.frame", row.names = c(NA, 
-7L))