如何在dolphindb中将多个列转成一列？

Question

在dolphindb中有这样一个表，代表了每个公司的各个产品种类的产品数量。

productType   company1    company2    company3
----------    --------    --------    --------
a             4           1           3
b             5           2           23
c             1           3           4
d             2           4           5

如何把上表转化成下表？

producType    companyName    amount
----------    -----------    ------
a             company1       4    
b             company1       5    
c             company1       1   
d             company1       2  
a             company2       1
b             company2       2
c             company2       3
d             company2       4
a             company3       3
b             company3       23
c             company3       4
d             company3       5

Answer 1

可以用unpivot函数，比如：

t = table(`a`b`c`d as productType, 4 5 1 2 as company1, 1 2 3 4 as company2, 3 23 4 5 as company3)
unpivot(t, `productType, `company1`company2`company3)