tidyverse包中count的用法

介绍
Description
count() lets you quickly count the unique values of one or more variables: df %>% count(a, b) is roughly equivalent to df %>% group_by(a, b) %>% summarise(n = n()). count() is paired with tally(), a lower-level helper that is equivalent to df %>% summarise(n = n()). Supply wt to perform weighted counts, switching the summary from n = n() to n = sum(wt).

add_count() and add_tally() are equivalents to count() and tally() but use mutate() instead of summarise() so that they add a new column with group-wise counts.

library(tidyverse)
glimpse(starwars)
#简单用法
starwars %>% count(species)
starwars %>% count(species, sort = TRUE)
starwars %>% count(sex, gender, sort = TRUE)#相当于table

starwars %>% count(birth_year, sort = TRUE)
starwars %>% count(birth_decade = round(birth_year, -1))

#count可以对最终结果进行加权
#构建数据集
df <- tribble(
  ~name,    ~gender,   ~runs,
  "Max",    "male",       10,
  "Sandra", "female",      1,
  "Susan",  "female",      4
)
# 未加权:
df %>% count(gender)
# 加权后:
df %>% count(gender, wt = runs)

# tally() 函数比count等级低，这个函数认为
starwars %>% tally()
starwars %>% group_by(species) %>% tally()

# both count() 和 tally() 类似，都有添加变量的作用，注意权重的情况
df %>% add_count(gender, wt = runs)
df %>% add_tally(wt = runs)
df %>% add_count(gender)