Elements¶

to which the answer is Everything.
— W.V.O. Quine, Word and Object

Line comment

q)/Oh what a lovely day


Trailing comment

q)2+2  /I know this one
4


Multiline comment

/
Oh what a beautiful morning
Oh what a wonderful day
\
a:42
\
ignore this and what follows
the restroom at the end of the universe


Nouns¶

noun examples
atom 42; "a"; 1b; 2012.08.04; ibm
vector (43;44;45); "abc"; 0101b; ibmgoo; 2012.09.15 2012.07.05
list (43;"44";45); ("abc";0101b;);(("abc";1 2 3); ibmabc)
dictionary abc!42 43 44; nameage!(johncarolted;42 43)
table ([]name:johncarolted; age:42 43 44)
keyed table ([name:johncarolted] age:42 43 44)

Atoms¶

An atom is a single number, character, boolean, symbol, timestamp… a single instance of any datatype.

Lists¶

Lists are zero or more items, separated by semicolons, and enclosed in parentheses. An item can be any noun.

q)count(42;ibm;2012.08.17)    /list of 3 items
3


A list may have 0, 1 or more items.

q)count()              /empty list
0
q)count enlist 42      /1-list
1
q)count(42;43;44;45)   /4-list
4


An atom is not a 1-list

A list with 1 item is not an atom. The enlist function makes a 1-list from an atom.


q)42~enlist 42
0b


A list item may be a noun, function or adverb.

q)count("abc";0000111111b;42)  /2 vectors and an atom
3
q)count(+;rotate;/)            /2 operators and an adverb
3


Vectors¶

In a vector (or simple list) all items are of the same datatype. Char vectors are also known as strings.

type example
numeric 42 43 44
date 2012.09.15 2012.07.05
char "abc"
boolean 0101b
symbol ibmattora

Attributes¶

Attributes are metadata that apply to lists of special form. They are often used on a dictionary domain or a table column to reduce storage requirements or to speed retrieval.
# Set attribute

For 64-bit V3.0+, where n is the number of items and d is the number of distinct (unique) items, the byte overhead in memory is:

s#2 2 3 sorted 0
u#2 4 5 unique 32*d
p#2 2 1 parted (48*d)+8*n
g#2 1 2 grouped (16*d)+8*n

Attribute u is for unique lists – where all items are distinct.

Grouped and parted

Attributes p and g are useful for lists in memory with a lot of repetition.

If the data can be sorted such that p can be applied, the p attribute effects better speedups than g, both on disk and in memory.

The g attribute implies an entry’s data may be dispersed – and possibly slow to retrieve from disk.

Some q functions use attributes to work faster:

Dictionaries¶

A dictionary is a map from a list of keys to a list of values. (The keys should be unique, though q does not enforce this.) The values of a dictionary can be any data structure.

q)/4 keys and 4 atomic values
q)bobcaroltedalice!42 39 51 44
bob  | 42
carol| 39
ted  | 51
alice| 44
q)/2 keys and 2 list values
q)show kids:namesages!(bobcaroltedalice;42 39 51 44)
names| bob carol ted alice
ages | 42  39    51  44


Tables¶

A dictionary in which the values are all lists of the same count can be flipped into a table.

q)count each kids
names| 4
ages | 4
q)tkids:flip kids  / flipped dictionary
names ages
----------
bob   42
carol 39
ted   51
alice 44


Or the table specified directly using table syntax, e.g.

q)/a flipped dictionary is a table
q)tkids~([]names:bobcaroltedalice; ages:42 39 51 44)
1b


Table syntax can declare one or more columns of a table as a key. The values of the key column/s of a table are unique.

q)([names:bobcarolbobalice;city:NYCCHISFOSFO]; ages:42 39 51 44)
names city| ages
----------| ----
bob   NYC | 42
carol CHI | 39
bob   SFO | 51
alice SFO | 44


Names and namespaces¶

A namespace is a container or context within which a name resolves to a unique value. Namespaces are children of the root namespace (usually just root) and are designated by a dot prefix. Names in the root have no prefix. The root namespace of a q session is parent to multiple namespaces, e.g. h, Q and z. (Namespaces with 1-character names – of either case – are reserved for use by Kx.)

q).z.p                         / UTC timestamp
2017.02.01D14:58:38.579614000


Namespaces are dictionaries

Namespace contents can be treated as dictionary entries.


q)v:5
q).ns.v:6
q).[v]      / value of v in root namespace
5
q).ns[v]    / value of v in ns
6
q).v       / indexed by juxtaposition
5
q).nsvv
6 6
q)..ns@\:v
5 6


Functions¶

Functions are:

1. operators and primitive functions, eg +, count
2. as defined in the lambda notation, eg {x+2*y}
3. as derived from (1) and (2) by adverbs, eg +/, count'
4. q-SQL functions, e.g. select

Functions are first-class objects and can be passed as arguments to other functions. Functions that take other functions as arguments are known as higher-order functions.

Reserved words¶

The following reserved words denote functions that are not also operators.

.Q.res (reserved words)

Operators¶

Operators are primitive binary functions that may be applied infix.

q)|[2;3]                 / maximum, prefix form
3
q)2|3                    / maximum, infix form
3
q)rotate[2;0 1 2 3 4 5]  / prefix form
2 3 4 5 0 1
q)2 rotate 0 1 2 3 4 5   / infix form
2 3 4 5 0 1


Operators are denoted by glyphs or reserved words or both – see note below on minimum and maximum. (They cannot be defined using the lambda notation.)

Glyphs¶

Minimum and maximum

The minimum operator is denoted by both the & glyph and the reserved word and. The maximum operator is denoted by both the | glyph and the reserved word or.

Reserved words¶

The following reserved words denote operators.

.Q.res (reserved words)

Adverbs are primitive higher-order functions: they return derivatives (derived functions). They are denoted by six overloaded glyphs: ', /, \, ':, /: and \:.

q)+/[2 3 4]  / reduce 2 3 4 with +
9
q)*/[2 3 4]  / reduce 2 3 4 with *
24


Control words¶

The control words do, if and while govern evaluation.

Views¶

A view is a calculation that is re-evaluated only if the values of the underlying dependencies have changed since its last evaluation. Views can help avoid expensive calculations by delaying propagation of change until a result is demanded.

The syntax for the definition is

q)viewname::[expression;expression;…]expression


The act of defining a view does not trigger its evaluation.

A view should not have side-effects, i.e. should not update global variables.

System commands¶

Expressions beginning with \ are system commands or multiline comments (see above).

q)/ load the script in file my_app.q
q)\l my_app.q


Scripts¶

A script is a text file; its lines a list of expressions and/or system commands, to be executed in sequence. By convention, script files have the extension q`.

Within a script

• function definitions may extend over multiple lines
• an empty comment begins a multiline comment.