Datatypes¶

Basic datatypes n c name sz literal null inf SQL Java .Net ------------------------------------------------------------------------------------ 0 * list 1 b boolean 1 0b Boolean boolean 2 g guid 16 0Ng UUID GUID 4 x byte 1 0x00 Byte byte 5 h short 2 0h 0Nh 0Wh smallint Short int16 6 i int 4 0i 0Ni 0Wi int Integer int32 7 j long 8 0j 0Nj 0Wj bigint Long int64 0 0N 0W 8 e real 4 0e 0Ne 0We real Float single 9 f float 8 0.0 0n 0w float Double double 0f 0Nf 10 c char 1 " " " " Character char 11 s symbol ` ` varchar 12 p timestamp 8 dateDtimespan 0Np 0Wp Timestamp DateTime (RW) 13 m month 4 2000.01m 0Nm 14 d date 4 2000.01.01 0Nd 0Wd date Date 15 z datetime 8 dateTtime 0Nz 0wz timestamp Timestamp DateTime (RO) 16 n timespan 8 00:00:00.000000000 0Nn 0Wn Timespan TimeSpan 17 u minute 4 00:00 0Nu 0Wu 18 v second 4 00:00:00 0Nv 0Wv 19 t time 4 00:00:00.000 0Nt 0Wt time Time TimeSpan

Columns: n short int returned by type and used for Cast, e.g. 9h$3 c character used lower-case for Cast and upper-case for Tok and Load CSV sz size in bytes inf infinity (no math on temporal types); 0Wh is 32767h

RO: read only; RW: read-write

Other datatypes 20-76 enums 77 anymap 104 projection 78-96 77+t – mapped list of lists of type t 105 composition 97 nested sym enum 106 f' 98 table 107 f/ 99 dictionary 108 f\ 100 lambda 109 f': 101 unary primitive 110 f/: 102 operator 111 f\: 103 iterator 112 dynamic load

Above, f is an applicable value.

Nested types are 77+t (e.g. 78 is boolean. 96 is time.)

The type is a short int:

zero for a general list
negative for atoms of basic datatypes
positive for everything else

Cast, Tok, type, .Q.ty (type)
Temporal data, Timezones

Basic types¶

The default type for an integer is long (7h or "j").

Before V3.0 it was int (6h or "i").

Strings¶

There is no string datatype. On this site, string is a synonym for character vector (type 10h). In q, the nearest equivalent to an atomic string is the symbol.

Strings can include multibyte characters, which each occupy the respective number of bytes. For example, assuming that the input encoding is UTF-8:

q){(x;count x)}"Zürich"
"Z\303\274rich"
7
q){(x;count x)}"日本"
"\346\227\245\346\234\254"
6

Other encodings may give different results.

q)\chcp
"Active code page: 850"
q)"Zürich"
"Z\201rich"

q)\chcp 1250
"Active code page: 1250"
q)"Zürich"
"Z\374rich"

Unicode

Temporal¶

The valid date range is 0001.01.01 to 9999.12.31. (Since V3.6 2017.10.23.)

The 4-byte datetime datatype (15) is deprecated in favour of the 8-byte timestamp datatype (12).

q)"D"$"3001.01.01"
3001.01.01

Internally, dates, times and timestamps are represented by integers:

q)show noon:`minutes`seconds`nanoseconds!(12:00;12:00:00;12:00:00.000000000)
minutes    | 12:00
seconds    | 12:00:00
nanoseconds| 0D12:00:00.000000000
q)"j"$noon
minutes    | 720
seconds    | 43200
nanoseconds| 43200000000000

Date calculations assume the proleptic Gregorian calendar.

Casting to timestamp from date or datetime outside of the timestamp supported year range results in ±0Wp. Out-of-range dates and datetimes display as 0000.00.00 and 0000.00.00T00:00:00:.000.

q)`timestamp$1666.09.02
-0Wp
q)0001.01.01-1
0000.00.00
q)"z"$0001.01.01-1 
0000.00.00T00:00:00.000

Valid ranges can be seen by incrementing or decrementing the infinities.

q)-0W 0Wp+1 -1      / limit of timestamp type
1707.09.22D00:12:43.145224194 2292.04.10D23:47:16.854775806

q)0p+ -0W 0Wp+1 -1  / timespan offset of those from 0p
-106751D23:47:16.854775806 106751D23:47:16.854775806

q)-0W 0Wn+1 -1      / coincide with the min/max for timespan

Symbols¶

A back tick ` followed by a series of characters represents a symbol, which is not the same as a string.

q)`symbol ~ "symbol"
0b

A back tick without characters after it represents the empty symbol: `.

Cast string to symbol

The empty symbol can be used with Cast to cast a string into a symbol, creating symbols whose names could not otherwise be written, such as symbols containing spaces. `$x is shorthand for "S"$x.

'world
q)s:`$"hello world"
q)s
`hello world

Q for Mortals: §2.4 Basic Data Types – Atoms

Filepaths¶

Filepaths are a special form of symbol.

q)count read0 `:path/to/myfile.txt  / count lines in myfile.txt

Infinities¶

Note that arithmetic for integer infinities (0Wh,0Wi,0Wj) is undefined, and does not retain the concept when cast.

q)0Wi+5
2147483652
q)0Wi+5i
-2147483644i
q)`float$0Wj
9.223372e+18
q)`float$0Wi
2.147484e+09

Arithmetic for float infinities (0we,0w) behaves as expected.

q)0we + 5
0we
q)0w + 5
0w

.Q.M (long infinity)

To infinity and beyond

Floating-point arithmetic follows IEEE754.

Integer arithmetic does no checks for infinities, just treats them as a signed integer.

q)vs[0b]@/:0N!0W+til 3
0W 0N -0W
0111111111111111111111111111111111111111111111111111111111111111b
1000000000000000000000000000000000000000000000000000000000000000b
1000000000000000000000000000000000000000000000000000000000000001b

but it does check for nulls.

q)10+0W+til 3
-9223372036854775799 0N -9223372036854775797

This can be abused to push infinities on nulls which then become sticky and can be filtered out altogether, e.g.

q)1+-1+-1+1+ -0W 0N 0W 1 2 3
0N 0N 0N 1 2 3

There is no display for short infinity.

q)0Wh
32767h
q)-0Wh
-32767h

Integer promotion is documented for Add.

Integer infinities

do not promote, other than the signed bit; there is no special treatment over any other int value
map to int_min+1 and int_max, with 0N as int_min; so there is no number smaller than 0N

Best practice is to view infinities as placeholders only, and not perform arithmetic on them.

Guid¶

The guid type (since V3.0) is a 16-byte type, and can be used for storing arbitrary 16-byte values, typically transaction IDs.

Generation

Use Deal to generate a guid (global unique: uses .z.a .z.i .z.p).

q)-2?0Ng
337714f8-3d76-f283-cdc1-33ca89be59e9 0a369037-75d3-b24d-6721-5a1d44d4bed5

If necessary, manipulate the bytes to make the uuid a Version-4 'standard' uuid.

Guids can also be created from strings or byte vectors, using sv or "G"$, e.g.

q)0x0 sv 16?0xff
8c680a01-5a49-5aab-5a65-d4bfddb6a661
q)"G"$"8c680a01-5a49-5aab-5a65-d4bfddb6a661"
8c680a01-5a49-5aab-5a65-d4bfddb6a661

0Ng is null guid.

q)0Ng
00000000-0000-0000-0000-000000000000
q)null 0Ng
1b

There is no literal entry for a guid, it has no conversions, and the only scalar primitives are =, < and > (similar to sym). In general, since V3.0, there should be no need for char vectors for IDs. IDs should be int, sym or guid. Guids are faster (much faster for =) than the 16-byte char vecs and take 2.5 times less storage (16 per instead of 40 per).

Other types¶

Enumerated types¶

Enumerated types are numbered from 20h up to 76h. For example, in a new session with no enumerations defined:

q)type `sym$10?sym:`AAPL`AIG`GOOG`IBM
20h
q)type `city$10?city:`london`paris`rome
20h

(Since V3.0, type 20h is reserved for `xxx$ where xxx is the name of a variable.)

Enumerate, Enumeration, Enum Extend
Enumerations

Nested types¶

These types are used for mapped lists of lists of the same type. The numbering is 77 + primitive type (e.g. 77 is anymap, 78 is boolean, 96 is time and 97 is `sym$ enumeration.)

q)`:t1.dat set 2 3#til 6
`:t1.dat
q)a:get `:t1.dat
q)type a            /integer nested type
83h
q)a
0 1 2
3 4 5

Dictionary and table¶

Dictionary is 99h and table is 98h.

q)type d:`a`b`c!(1 2;3 5;7 11)     / dict
99h
q)type flip d                      / table
98h

Functions, iterators, derived functions¶

Functions, lambdas, operators, iterators, projections, compositions and derived functions have types in the range [100–112].

q)type each({x+y};neg;-;\;+[;1];<>;,';+/;+\;prev;+/:;+\:;`f 2:`f,1)
100 101 102 103 104 105 106 107 108 109 110 111 112h