如何获取数据中首先出现的第一行？

Question

我有一个如下所示的数据集：

data <- tribble(
  ~shop_name, ~products, ~category_name,
  "A",         1,          "Game",
  "A",         1,          "Book",         
  "A",         2,          "Electronic",
  "A",         3,          "Home", 
  "B",         5,          "Game",
  "B",         5,          "Electronic",
  "B",         8,          "Home",
  "C",         1,          "Book",
  "C",         7,          "Game",
  "C",         9,          "Game",
)

我想查看基于产品的前 1 个类别，并编码：

data %>% 
  group_by(shop_name) %>% 
  top_n(1, products) %>% 
  mutate(top_category = toString(category_name))

但由于产品有时每个 shop_name 具有相同的值，因此“top_category”中有多个类别名称。如何获取数据集中最先出现的第一行？

Answer 1

使用dplyr::first:

data %>% 
  group_by(shop_name) %>% 
  summarise(products = first(products),
            category_name = first(category_name))

保留所有列而不明确指定它们

data %>% 
  group_by(shop_name) %>% 
  summarise_all(first)

输出

# shop_name products category_name
#  <chr>        <dbl> <chr>        
# 1 A                1 Game         
# 2 B                5 Game         
# 3 C                1 Book 

Answer 2

data %>% 
  group_by(shop_name) %>% 
  top_n(1, desc(products)) %>%
  plyr::ddply( "shop_name", head, 1)

  shop_name products category_name
1         A        1          Game
2         B        5          Game
3         C        1          Book