按组划分的两个日期之间的平均值

Question

我有两个数据框，一个包含每天和相机的值 (df1)，另一个包含每个相机的日期范围 (df2)。我需要在 df2 的日期范围内为每个相机平均 df1 中的值。

**这是我的数据的一个非常简化的版本。我有大约 300 个摄像头，每个摄像头有多个日期范围，我需要为其取平均值。

df1 <- data.frame(camera=c("Cam 1","Cam 1","Cam 1","Cam 2","Cam 2","Cam 2","Cam 3","Cam 3","Cam 3"),
date=c("2011-03-15","2011-03-16","2011-03-17","2011-03-15","2011-03-16","2011-03-17","2011-03-17","2011-03-18","2011-03-19"),
value=c(1,0,2,3,1,2,2,1,0))

df1$date <- as.Date(df1$date,format='%Y-%m-%d')

df2 <- data.frame(camera=c("Cam 1","Cam 2","Cam 3"),
start_date=c("2011-03-15", "2011-03-15","2011-03-17"),
end_date=c("2011-03-17","2011-03-17","2011-03-19"))

df2$start_date <- as.Date(df2$start_date,format='%Y-%m-%d')
df2$end_date <- as.Date(df2$end_date,format='%Y-%m-%d')

我遇到的问题是多个相机的值相同相机）。我正在使用 dplyr 和 tidyr 包，我认为按相机分组可以解决这个问题，但事实并非如此。我也使用 mutate 或 summarise 函数得到相同的结果。我发现在一个日期范围内或按组求平均值有很多帮助，但不是两者兼而有之。任何帮助将不胜感激！这是我的代码：

 average<-df2 %>%
  group_by(camera, start_date, end_date) %>%
  mutate(avg= mean(df1$value[between(df1$date, start_date, end_date)])) %>%
  ungroup

我得到了这样一张桌子：

camera	start_date	end_date	avg
Cam 1	2011-03-15	2011-03-17	1.57
Cam 2	2011-03-15	2011-03-17	1.57
Cam 3	2011-03-17	2011-03-19	1.40

当我想要这个时：

camera	start_date	end_date	avg
Cam 1	2011-03-15	2011-03-17	1
Cam 2	2011-03-15	2011-03-17	2
Cam 3	2011-03-17	2011-03-19	1

Answer 1

我们可以使用非等值连接

library(data.table)
setDT(df1)[, .(start_date = date, end_date = date, camera,
     value)][df2, .(avg = mean(value)),
    on = .(camera, start_date >= start_date,
        end_date <= end_date), by = .EACHI]

-输出

   camera start_date   end_date avg
1:  Cam 1 2011-03-15 2011-03-17   1
2:  Cam 2 2011-03-15 2011-03-17   2
3:  Cam 3 2011-03-17 2011-03-19   1

---

或使用tidyverse

library(dplyr)
library(fuzzyjoin)
fuzzy_left_join(df1, df2, by = c("camera", "date" = "start_date", 
       "date" = "end_date"), match_fun = list(`==`, `>=`, `<=`)) %>%
    group_by(camera = camera.x, start_date, end_date) %>% 
    summarise(avg = mean(value), .groups = 'drop')

-输出

# A tibble: 3 x 4
  camera start_date end_date     avg
  <chr>  <date>     <date>     <dbl>
1 Cam 1  2011-03-15 2011-03-17     1
2 Cam 2  2011-03-15 2011-03-17     2
3 Cam 3  2011-03-17 2011-03-19     1