我有一个data.table，其格式如下：
date action cnt
1: 2016-06-14 PICK_APPLE 2
2: 2016-06-15 PICK_APPLE 12
3: 2016-06-16 PICK_APPLE 7
4: 2016-06-17 PICK_APPLE 5
5: 2016-08-10 PICK_APPLE 1
6: 2016-08-11 PICK_APPLE 1
7: 2016-08-14 PICK_APPLE 1
8: 2016-08-17 PICK_APPLE 7
9: 2016-08-19 PICK_APPLE 1
10: 2016-08-21 PICK_APPLE 2
11: 2016-08-22 PICK_APPLE 3
12: 2016-08-23 PICK_APPLE 12
13: 2016-08-24 PICK_APPLE 6
14: 2016-08-30 PICK_APPLE 4
15: 2016-08-31 PICK_APPLE 4
16: 2016-09-05 PICK_APPLE 8
17: 2016-09-08 PICK_APPLE 1
18: 2016-08-23 PICK_ORANGE 1
19: 2016-08-31 PICK_ORANGE 2
20: 2016-09-05 PICK_ORANGE 2
21: 2016-08-05 ATE_APPLE 1
22: 2016-08-14 ATE_APPLE 1
23: 2016-08-17 ATE_APPLE 1
24: 2016-08-18 ATE_APPLE 1
25: 2016-08-30 ATE_APPLE 3
date action cnt
我想创建一个表，其中列名称为action列中的唯一值，行名称为date列中的唯一值。例如，结果应该是：
date PICK_APPLE PICK_ORANGE ATE_APPLE
1: 2016-06-14 2
2: 2016-06-15 12
3: 2016-06-16 7
4: 2016-06-17 5
21: 2016-08-05 1
5: 2016-08-10 1
6: 2016-08-11 1
7: 2016-08-14 1 1
8: 2016-08-17 7 1
24: 2016-08-18 1
9: 2016-08-19 1
10: 2016-08-21 2
11: 2016-08-22 3
12: 2016-08-23 12 1
13: 2016-08-24 6
14: 2016-08-30 4
15: 2016-08-31 4 2
16: 2016-09-05 8
17: 2016-09-08 1
20: 2016-09-05 2
date PICK_APPLE PICK_ORANGE ATE_APPLE
是否有标准方法可以执行此操作，或者我是否需要循环执行每个(date,action)组合？