计算 DolphinDB 中的连续前面元素

Question

Volume	f	Explanation
10	0	no volume before 10
7	0	no smaller volume before 7
13	2	Both 10 and 7 are smaller than 13
6	0	13 is larger than 6
4	0	6 is larger than 4
8	2	Both 6 and 4 are smaller than 8
7	0	8 is larger than 7
3	0	7 is larger than 3
4	1	3 is smaller than 4

如上表所示，我想在 DolphinDB 中根据体积获取 f 列。 假设当前卷为 t，期望输出 f 为满足以下条件的卷数：

1. volume 列中有连续的元素小于 t
2. 连续元素的最后一卷是前一卷 在 t 之前；

详细的计算原理在说明栏中有说明。

我尝试了 for-loop，但它不起作用。 DolphinDB 是否支持任何其他函数来获取结果？

Answer 1

t = table(1..10 as volume) tmp = select volume, iif(deltas(volume)>0, rowNo(volume), NULL) as flag from t tmp.bfill!() select volume, cumrank(volume) from tmp context by flag