$ Enumerate
Syntax: x$y, $[x;y]
Where
xandyare listsx~distinct x- items of
yare all items ofx
returns y as an enumeration of x.
Using built-in Enumerate:
q)show e:`x$y;
`x$`a`b`c`b`a`b`c`c`c`c`c`c`c
Values are stored as indexes and so need less space.
q)"i"$e
0 1 2 1 0 1 2 2 2 2 2 2 2i
Changing one lookup value (in x) has the same effect as changing those values in the enumeration, while the indexes backing e are unchanged.
q)x[0]:`o
q)e
x$`o`b`c`b`o`b`c`c`c`c`c`c`c
q)"i"$e
0 1 2 1 0 1 2 2 2 2 2 2 2i
To get x and y from e:
q)(key;value)@\:e
`x
`o`b`c`b`o`b`c`c`c`c`c`c`c
Ensure all items of y are in x
When creating an enumeration using $, the domain of the enumeration must be in x, otherwise a cast error will be signalled.
q)y:`a`b`c`b`a`b`c`c`c`c`c`c`c
q)x:`a`b
q)`x$y
'cast
To expand the domain, use ? (Enum Extend) instead of $.
Errors
| error | cause |
|---|---|
| cast | item/s of y not in x |
Enum Extend,
Enumeration,
$ dollar
Enumerations
Q for Mortals
§7.5 Enumerations ,
§8.5 Foreign Keys and Virtual Columns