使用相同的参考比较组内的日期

Question

我有一个针对不同患者的数据表("Spell")和每个患者的几个温度("Temp")测量值("Episode").我也有每个温度的日期和时间.

Spell Episode         Date    Temp
 1       3       2-1-17 21:00   40
 1       2       2-1-17 20:00   36
 1       1       1-1-17 10:00   37
 2       3       2-1-17 15:00   36
 2       2       2-1-17 10:00   37
 2       1       1-1-17 8:00    36
 3       1       3-1-17 10:00   40
 4       3       4-1-17 15:00   36
 4       2       3-1-17 12:00   40
 4       1       3-1-17 10:00   39
 5       7       3-1-17 17:30   36
 5       6       2-1-17 17:00   36
 5       5       2-1-17 16:00   37
 5       1       1-1-17 9:00    36
 5       4       1-1-17 14:00   39
 5       3       1-1-17 13:00   40
 5       2       1-1-17 11:00   39

我有兴趣在最后一次测量之前24小时完成所有测量,我已经用法术和反向日期对观测值进行了分组,但我不确定如何使用相同的参考进行组内比较(在这种情况下,每组的第一行).结果应该是:

    Spell Episode         Date    Temp
 1       3       2-1-17 21:00   40
 1       2       2-1-17 20:00   36
 2       3       2-1-17 15:00   36
 2       2       2-1-17 10:00   37
 3       1       3-1-17 10:00   40
 4       3       4-1-17 15:00   36
 5       7       3-1-17 17:30   36

非常感谢能指出正确方向的任何想法.

编辑:日期为dm-yy H:M格式.这是来自数据的输入:

structure(list(Spell = c(1L, 1L, 1L, 2L, 2L, 2L, 3L, 4L, 4L, 
4L, 5L, 5L, 5L, 5L, 5L, 5L, 5L), Episode = c(3L, 2L, 1L, 3L, 
2L, 1L, 1L, 3L, 2L, 1L, 7L, 6L, 5L, 1L, 4L, 3L, 2L), Date = c("2-1-17 21:00", 
"2-1-17 20:00", "1-1-17 10:00", "2-1-17 15:00", "2-1-17 10:00", 
"1-1-17 8:00", "3-1-17 10:00", "4-1-17 15:00", "3-1-17 12:00", 
"3-1-17 10:00", "3-1-17 17:30", "2-1-17 17:00", "2-1-17 16:00", 
"1-1-17 9:00", "1-1-17 14:00", "1-1-17 13:00", "1-1-17 11:00"
), Temp = c(40L, 36L, 37L, 36L, 37L, 36L, 40L, 36L, 40L, 39L, 
36L, 36L, 37L, 36L, 39L, 40L, 39L)), .Names = c("Spell", "Episode", 
"Date", "Temp"), class = c("data.table", "data.frame"), row.names = c(NA, 
-17L), .internal.selfref = <pointer: 0x00000000001f0788>)

Answer 1

library(dplyr)

df %>% 
  mutate(Date2 = as.numeric(strptime(df$Date, "%d-%m-%Y %H:%M"))) %>% 
  group_by(Spell) %>% 
  filter(Date2 >= (max(Date2) - 60*60*24)) %>%
  select(-Date2)

Answer 2

解决方案仅使用data.table:

# convert Date column to POSIXct
DT[,Date:=as.POSIXct(Date,format='%d-%m-%y %H:%M',tz='GMT')]
# filter the data.table
filteredDT <- DT[, .SD[as.numeric(difftime(max(Date),Date,units='hours')) <= 24], by = Spell]

> filteredDT
   Spell Episode                Date Temp
1:     1       3 2017-01-02 21:00:00   40
2:     1       2 2017-01-02 20:00:00   36
3:     2       3 2017-01-02 15:00:00   36
4:     2       2 2017-01-02 10:00:00   37
5:     3       1 2017-01-03 10:00:00   40
6:     4       3 2017-01-04 15:00:00   36
7:     5       7 2017-01-03 17:30:00   36