使用 dplyr 从起止范围变量按月汇总计数

创建一个列表列，其中包含每组日期之间的月序列，然后是Unest和count.

笔记:

1. 我用lubridate::floor_date()把enrollment_start四舍五入到一个月的第一天.否则，如果enrollment_start在当月29日或更晚，则seq()可能会跳过月份.
2. 示例数据的第五行中的enrollment_start比enrollment_end晚——我假设这是一个错误，并将其删除.

library(tidyverse)
library(lubridate)

enrollments %>% 
  mutate(
    across(c(enrollment_start, enrollment_end), dmy),  # convert to date
    month = map2(
      floor_date(enrollment_start, unit = "month"),    # round to 1st day
      enrollment_end,
      ~ seq(.x, .y, by = "month")
    )
  ) %>% 
  unnest_longer(month) %>% 
  count(month, name = "enrollment_count")

#> # A tibble: 27 x 2
#>    month      enrollment_count
#>    <date>                <int>
#>  1 2017-01-01                2
#>  2 2017-02-01                2
#>  3 2017-03-01                1
#>  4 2017-04-01                2
#>  5 2017-05-01                2
#>  6 2017-06-01                3
#>  7 2017-07-01                3
#>  8 2017-08-01                3
#>  9 2017-09-01                3
#> 10 2017-10-01                3
#> # ... with 17 more rows

^{由reprex package(v2.0.1)于2022-03-25创建}