2.7 非重复计数
序表中数据聚合时，非重复计数。分析数据文件中哪个字段最适合被设定为主键列。
| PassengerId | Survived | Pclass | Name | Sex | Age |
|---|---|---|---|---|---|
| 1 | 0 | 3 | “Braund, Mr. Owen Harris” | male | 22 |
| 2 | 1 | 1 | “Cumings, Mrs. John Bradley” | female | 38 |
| 3 | 1 | 3 | “Heikkinen, Miss. Laina” | female | 26 |
| 4 | 1 | 1 | “Futrelle, Mrs. Jacques Heath” | female | 35 |
| 5 | 0 | 3 | “Allen, Mr. William Henry” | male | 35 |
| 6 | 0 | 3 | “Moran, Mr. James” | male | |
| 7 | 0 | 1 | “McCarthy, Mr. Timothy J” | male | 54 |
| … | … | … | … | … | … |
脚本：
| A | |
|---|---|
| 1 | =T(“titanic_train.xlsx”) |
| 2 | =A1.fno().new(A1.fname(~):Name,A1.field(~).icount():DCount) |
| 3 | =A2.select(DCount==A1.len()) |
A2 使用 icount() 函数计算每个字段的非重复成员的数量
A3 选出非重复计数与全部数据长度相同的字段
