CODEWITHSUNDEEP
kdb+
stupidkidyoyo
stupidkidyoyo

Reputation: 21

#q #kdb+ What is the difference between table and dictionaries

What is the difference between table and dictionaries in kdb+? Can you explain why such differences are necessary and what are they good for?

Upvotes: 2

Views: 616

Answers (2)

terrylynch
terrylynch

Reputation: 13657

A dictionary can be any arbitrary mapping of keys to values with no restrictions on types, e.g.

q)d:(`abc;1i;.z.D)!(2j;`xyz;.z.P)
q)d[`abc]
2
q)d[2021.03.01]
2021.03.01D06:11:47.519373000

A list of dictionaries which specifically have symbols as keys, have the same keys and have consistent datatypes is promoted to a table. Tables then give you the ability to perform q-sql (select/update/delete) syntax and all of the other advantages that tables bring (persistence, joins).

q)(`abc`def!1 2;`abc`def!3 4)
abc def
-------
1   2
3   4

Dictionaries are still very useful for lookups, mappings, replacements etc

Upvotes: 1

Matt Moore
Matt Moore

Reputation: 2800

A table is actually a list of dictionaries. E.g.

t:([]sym:`a`b`c;price:1 2 3f)
first t
sym  | `a
price| 1f

Upvotes: 2

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