Casting & encoding
Casting converts data from one datatype to another.
$ (cast)¶
Syntax: x $ y
Where x is a lower-case letter, symbol or non-negative short, returns y cast according to x. A table of x values for cast:
q)flip{(x;.Q.t x;key'[x$\:()])}5h$where" "<>20#.Q.t
1h "b" `boolean
2h "g" `guid
4h "x" `byte
5h "h" `short
6h "i" `int
7h "j" `long
8h "e" `real
9h "f" `float
10h "c" `char
11h "s" `symbol
12h "p" `timestamp
13h "m" `month
14h "d" `date
15h "z" `datetime
16h "n" `timespan
17h "u" `minute
18h "v" `second
19h "t" `time
Cast to integer:
q)"i"$10
10i
q)(`int;"i";6h)$10
10 10 10i
Cast to boolean:
q)1h$1 0 2
101b
Find parts of time:
q)`hh`uu`ss$03:55:58.11
3 55 58i
q)show timestamp:.z.p
2018.01.05D14:14:34.728805000
q)`year`dd`mm`hh`uu`ss$timestamp
2018 5 1 14 14 34i
q)timestamp.year
2018i
| year | month | mm | week | dd | hh | uu | ss
--------------------------------------------------------
timestamp | x | x | x | x | x | x | x | x
month | x | x | x | | | | |
date | x | x | x | x | x | | |
datetime | x | x | x | x | x | x | x | x
timespan | | | | | | x | x | x
minute | | | | | | x | x | x
second | | | | | | x | x | x
time | | | | | | x | x | x
milliseconds: "i"$time mod 1000
milliseconds: "i"$mod[;1000]"t"$datetime
nanoseconds: "i"$timestamp mod 1000000000
Casting string to symbol
When converting a string to a symbol, leading and trailing blanks are automatically trimmed:
q)`$" IBM "
`IBM
Identity:
q)("*";0h)$1
10 10
q)("*";0h)$\:"2012-02-02"
"2012-02-02"
"2012-02-02"
To infinity and beyond!
Casting an infinity from a narrower to a wider datatype does not always return another infinity.
q)`float$0Wh
32767f
x is min 0#x.
\: (int to byte)¶
Syntax: 0x0\:x
Where x is an int.
q)0x0\:1234605616436508552
0x1122334455667788
FIXME Signals '\:
! (ints to enum)¶
Syntax: `x!y
Where `x is the name of a symbol list and y is a non-negative int list, returns an enumerated symbol list.
q)x:`a`b`c`d
q)`x!1 2 3
`x$`b`c`d
string¶
Syntax: string x
Returns each item in list x as a string; applies to all data types.
q)string `ibm`goog
"ibm"
"goog"
q)string 2 7 15
,"2"
,"7"
"15"
q)string (2 3;"abc")
(,"2";,"3")
(,"a";,"b";,"c")
It applies to the values of a dictionary, and the columns of a table:
q)string `a`b`c!2002 2004 2010
a| "2002"
b| "2004"
c| "2010"
q)string ([]a:1 2 3;b:`ibm`goog`aapl)
a b
-----------
,"1" "ibm"
,"2" "goog"
,"3" "aapl"
.h.iso8601, .Q.addr (IP address), .Q.f (format), .Q.fmt (format)
sv¶
Syntax: x sv y
Decode – where
- (base to integer)
xandyare numeric,yis evaluated to basex, which may be a list.
q)10 sv 2 3 5 7
2357
q)100 sv 2010 3 17
20100317
q)0 24 60 60 sv 2 3 5 7 / 2 days, 3 hours, 5 minutes, 7 seconds
183907
Note
when x is a list, the first number is not used. The calculation is done as:
q)baseval:{y wsum reverse prds 1,reverse 1_x}
q)baseval[0 24 60 60;2 3 5 7]
183907f
- (bytes to integer)
xis0x0andyis a vector of bytes of length 2, 4 or 8, returnsyconverted to the corresponding integer.
q)0x0 sv "x" $0 255 / short
255h
q)0x0 sv "x" $128 255
-32513h
q)0x0 sv "x" $0 64 128 255 / int
4227327
q)0x0 sv "x" $til 8 / long
283686952306183j
q)256j sv til 8 / same calculation
283686952306183j
Converting non integers
Use 1: – eg:
q)show a:0x0 vs 3.1415
0x400921cac083126f
q)(enlist 8;enlist "f")1: a /float
3.1415
- (bits to integer)
xis0bandyis a boolean vector of length 8, 16, 32, or 64, returnsyconverted to the corresponding integer or — in the case of 8 bits — a byte value.
q)0b sv 64#1b
-1
q)0b sv 32#1b
-1i
q)0b sv 16#1b
-1h
q)0b sv 8#1b
0xff
$ (tok)¶
Syntax: x $ y
Where x is an upper-case letter or non-positive short, and y is a string, returns y interpreted as a value according to x.
A table of x values for tok:
q)flip{(neg x;upper .Q.t x;key'[x$\:()])}5h$where" "<>20#.Q.t
-1h "B" `boolean
-2h "G" `guid
-4h "X" `byte
-5h "H" `short
-6h "I" `int
-7h "J" `long
-8h "E" `real
-9h "F" `float
-10h "C" `char
-11h "S" `symbol
-12h "P" `timestamp
-13h "M" `month
-14h "D" `date
-15h "Z" `datetime
-16h "N" `timespan
-17h "U" `minute
-18h "V" `second
-19h "T" `time
String to symbol
Use `$y as shorthand for "S"$y.
q)"S"$"hello"
`hello
q)`$"hello"
`hello
q)"E"$"3.14"
3.14e
q)-8h$"3.14"
3.14e
q)"D"$"2000-12-12"
2000.12.12
q)"U"$"12:13:14"
12:13
q)"T"$"123456789"
12:34:56.789
q)"P"$"2015-10-28D03:55:58.6542"
2015.10.28D03:55:58.654200000
q)"I"$"192.168.1.34" /an IP address as an int
-1062731486i
Truthy characters
These characters are recognized as boolean true:
q).Q.an where"B"$'.Q.an
"txyTXY1"
Parsing Unix timestamps (from seconds since Unix epoch), string with 9…11 digits:
q)"P"$"10129708800"
2290.12.31D00:00:00.000000000
q)"P"$"00000000000"
1970.01.01D00:00:00.000000000
If these digits are followed by a . it will parse what follows . as parts of second, e.g.
q)"P"$"10129708800.123456789"
2290.12.31D00:00:00.123456789
q)"P"$"00000000000.123456789"
1970.01.01D00:00:00.123456789
"D"$ will tok dates with varied formats:
[yy]yymmdd
ddMMM[yy]yy
yyyy/[mm|MMM]/dd
[mm|MMM]/dd/[yy]yy / \z 0
dd/[mm|MMM]/[yy]yy / \z 1
vs¶
Syntax: x vs y
Encode – where:
xis0bandyis an integer, returns the bit representation ofy.
q)0b vs 23173h
0101101010000101b
q)0b vs 23173
00000000000000000101101010000101b
xis0x0andyis a number, returns the internal representation ofy, with each byte in hex.
q)0x0 vs 2413h
0x096d
q)0x0 vs 2413
0x0000096d
q)0x0 vs 2413e
0x4516d000
q)0x0 vs 2413f
0x40a2da0000000000
q)"."sv string"h"$0x0 vs .z.a / ip address string from .z.a
"192.168.1.213"
xandyare integer, the result is the representation ofyin basex. (Since V3.4t 2015.12.13.)
q)10 vs 1995
1 9 9 5
q)2 vs 9
1 0 0 1
q)24 60 60 vs 3805
1 3 25
q)"." sv string 256 vs .z.a / ip address string from .z.a
"192.168.1.213"
If y is an integer vector then the result is a matrix with count[x] items whose ith column (x vs y)[;i] is identical to x vs y[i]. More generally, y can be any list of integers, and each item of the result is identical to y in structure.
q)a:10 vs 1995 1996 1997
q)a
1 1 1
9 9 9
9 9 9
5 6 7
q)a[;0]
1 9 9 5
q)10 vs(1995;1996 1997)
1 1 1
9 9 9
9 9 9
5 6 7
.Q.j10 (encode binhex), .Q.x10 (decode binhex), .Q.j12 (encode base64), .Q.x12 (decode base64)