我有一个数据框：
dput(x)
structure(list(ymd = structure(c(1446336000, 1446336000, 1446336000,
1446336000, 1446336000, 1446336000, 1446336000, 1446336000, 1446422400,
1446422400, 1446422400, 1446422400, 1446422400, 1446422400, 1446422400,
1446422400, 1446508800, 1446508800, 1446508800, 1446508800, 1446508800,
1446508800, 1446508800, 1446508800), class = c("POSIXct", "POSIXt"
), tzone = "UTC"), id = c(2, 9, 13, 15, 20, 24, 27, 41, 2, 9,
13, 15, 20, 24, 27, 41, 2, 9, 13, 15, 20, 24, 27, 41), value = c(2865,
3015, 4365, 6015, 4515, 1815, 765, 5115, 2865, 3015, 5565, 6015,
4515, 1815, 765, 4965, 2865, 3015, 5565, 6015, 4515, 1815, 765,
2715)), .Names = c("ymd", "id", "value"), row.names = c(NA, 24L
), class = "data.frame")
> x
ymd id value
1 2015-11-01 2 2865
2 2015-11-01 9 3015
3 2015-11-01 13 4365
4 2015-11-01 15 6015
5 2015-11-01 20 4515
6 2015-11-01 24 1815
7 2015-11-01 27 765
8 2015-11-01 41 5115
9 2015-11-02 2 2865
10 2015-11-02 9 3015
11 2015-11-02 13 5565
12 2015-11-02 15 6015
13 2015-11-02 20 4515
14 2015-11-02 24 1815
15 2015-11-02 27 765
16 2015-11-02 41 4965
17 2015-11-03 2 2865
18 2015-11-03 9 3015
19 2015-11-03 13 5565
20 2015-11-03 15 6015
21 2015-11-03 20 4515
22 2015-11-03 24 1815
23 2015-11-03 27 765
24 2015-11-03 41 2715
并希望获得一个表格，显示每个ID的值，随着时间的推移。 所以行是id，列是日期（ymd）。细胞值将是值。
我看起来像这样：
id 2015-11-01 2015-11-02 2015-11-03
2 2865 2865 2865
9 3015 3015 3015
13 4365 ...
...
我试着玩重塑，但无法理解。
答案 0 :(得分：2)
library(reshape2)
dcast(x, id~ymd)
# id 2015-11-01 2015-11-02 2015-11-03
# 1 2 2865 2865 2865
# 2 9 3015 3015 3015
# 3 13 4365 5565 5565
# 4 15 6015 6015 6015
# 5 20 4515 4515 4515
# 6 24 1815 1815 1815
# 7 27 765 765 765
# 8 41 5115 4965 2715