如何基于 R 中长格式的数据框创建具有不同列长度的 Markdown 表？

Question

我正在处理一个 R Markdown 文件，我想将其作为手稿提交给学术期刊。我想创建一个表格，显示哪些三个词（item2）与一些关键字（item1）最常同时出现。请注意，某些关键词有超过三个同时出现的词。我目前正在使用的数据：

item1 <- c("water","water","water","water","water","sun","sun","sun","sun","moon","moon","moon")
item2 <- c("tree","dog","cat","fish","eagle","bird","table","bed","flower","house","desk","tiger")
n <- c("200","83","34","34","34","300","250","77","77","122","46","46")
df <- data.frame(item1,item2,n)

这给出了这个数据框：

   item1  item2   n
1  water   tree 200
2  water    dog  83
3  water    cat  34
4  water   fish  34
5  water  eagle  34
6    sun   bird 300
7    sun  table 250
8    sun    bed  77
9    sun flower  77
10  moon  house 122
11  moon   desk  46
12  moon  tiger  46

最终，我想将数据传递给函数papaja::apa_table，这需要一个data.frame（或矩阵/列表）。因此，我需要重塑数据。

我的问题： 如何重塑数据（最好使用dplyr）以获得以下结构？

  water_item2 water_n sun_item2 sun_n moon_item2 moon_n
1        tree     200      bird   300      house    122
2         dog      83     table   250       desk     46
3         cat      34       bed    77      tiger     46
4        fish      34    flower    77       <NA>   <NA>
5       eagle      34      <NA>  <NA>       <NA>   <NA>

Answer 1

我们可以从old answer of mine 借用一种方法来解决不同的问题，并修改经典的gather()、unite()、spread() 策略，方法是按组创建唯一标识符以避免重复标识符，然后删除该变量：

library(dplyr)
library(tidyr)

item1 <- c("water","water","water","water","water","sun","sun","sun","sun","moon","moon","moon")
item2 <- c("tree","dog","cat","fish","eagle","bird","table","bed","flower","house","desk","tiger")
n <- c("200","83","34","34","34","300","250","77","77","122","46","46")
# Owing to Richard Telford's excellent comment,
# I use data_frame() (or equivalently for our purposes,
# data.frame(..., stringsAsFactors = FALSE))
# to avoid turning the strings into factors

df <- data_frame(item1,item2,n)

df %>% 
    group_by(item1) %>%
    mutate(id = 1:n()) %>%
    ungroup() %>%
    gather(temp, val, item2, n) %>%
    unite(temp2, item1, temp, sep = '_') %>%
    spread(temp2, val) %>%
    select(-id)

# A tibble: 5 x 6
  moon_item2 moon_n sun_item2 sun_n water_item2 water_n
  <chr>      <chr>  <chr>     <chr> <chr>       <chr>  
1 house      122    bird      300   tree        200    
2 desk       46     table     250   dog         83     
3 tiger      46     bed       77    cat         34     
4 NA         NA     flower    77    fish        34     
5 NA         NA     NA        NA    eagle       34