Conforming Dictionaries

Question

What are conforming dictionaries?

Given the following dictionaries:

A:`a`b!10 20
B:`a`b!20 30

Explain why:

(A;B)

produces a table.

Also explain why the following does not produce a table:

A:`a`b!10 20
B:`b`a!20 30

(A;B)

Solution

A:`a`b!10 20
B:`a`b!20 30
(A;B)

a  b
-----
10 20
20 30

A and B conform — same keys, `a`b, in the same order — so q promotes the list to a table (type (A;B) is 98h).

Alternative Solution

A:`a`b!10 20
B:`b`a!20 30
(A;B)

`a`b!10 20
`b`a!20 30

Here the key names match but the order doesn't (`a`b vs `b`a), so the dictionaries don't conform — (A;B) stays a plain 2-item list of dictionaries.

Explanation

The only requirement for auto-promotion is matching keys in matching order — value types are irrelevant. E.g. B:`a`b!("hjk";"ghj") still conforms with A:`a`b!10 20, producing a table whose columns a and b are general (mixed) lists.