我想以相同的时间间隔创建一个具有不同ID值的数据框，如果该值不存在，我必须携带该特定ID的最后一个值。这是我的数据框
df
ID FROM TO VALUE
1 a 2014-09-24 20:00:52 2014-09-24 20:00:52 121.9000
2 a 2014-09-24 20:02:38 2014-09-24 20:02:39 111.9000
3 a 2014-09-24 20:13:46 2014-09-24 20:13:48 120.9000
4 b 2014-09-24 20:00:52 2014-09-24 20:00:52 113.5631
5 b 2014-09-24 20:02:38 2014-09-24 20:02:38 112.5631
6 b 2014-09-24 20:13:39 2014-09-24 20:13:49 110.5631
从2014-09-24 20:02:38到2014-09-24 20:02:39，a的价值为111.9000。我希望将df的输出作为
a b FROM TO
121.9000 113.5631 2014-09-24 20:00:52 2014-09-24 20:00:52
111.9000 112.5631 2014-09-24 20:02:38 2014-09-24 20:02:38
111.9000 110.5631 2014-09-24 20:13:39 2014-09-24 20:13:45 # a's value is carry forward
120.9000 110.5631 2014-09-24 20:13:46 2014-09-24 20:13:49
任何有效的方法来实现上述结果。谢谢。
dput(df)
structure(list(ID = c("a", "a", "a", "b", "b", "b"), FROM = c("2014-09-24 20:00:52",
"2014-09-24 20:02:38", "2014-09-24 20:13:46", "2014-09-24 20:00:52",
"2014-09-24 20:02:38", "2014-09-24 20:13:39"), TO = c("2014-09-24 20:00:52",
"2014-09-24 20:02:39", "2014-09-24 20:13:48", "2014-09-24 20:00:52",
"2014-09-24 20:02:38", "2014-09-24 20:13:49"), VALUE = c(121.899978637695,
111.899978637695, 120.899978637695, 113.563064575195, 112.563064575195,
110.563064575195)), .Names = c("ID", "FROM", "TO", "VALUE"), row.names = c(NA,
-6L), class = "data.frame")