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$ Cast

Convert to another datatype

x$y     $[x;y]

Where x is:

  • a positive short, lower-case letter, or symbol from the following table, returns y cast according to x

    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
12h "p" `timestamp
13h "m" `month
14h "d" `date
15h "z" `datetime
16h "n" `timespan
17h "u" `minute
18h "v" `second
19h "t" `time

  • a symbol from the list `year`dd`mm`hh`uu`ss and y is a temporal type, returns the year, day, month, hour, minute, or seconds value from y as tabulated below

  • 0h or "*", and y is not a string, returns y (Identity)

  • an upper-case letter or a negative short int, see Tok

Casting does not change the underlying bit pattern of the data, only how it is represented.

Iteration

Cast is an atomic function.

q)12 13 14 15 16 17 18 19h$42
2000.01.01D00:00:00.000000042
2003.07m
2000.02.12
2000.02.12T00:00:00.000
0D00:00:00.000000042
00:42
00:00:42
00:00:00.042

q)(12h;"m";`date)$42
2000.01.01D00:00:00.000000042
2003.07m
2000.02.12

q)(12h;"m";`date)$42 43 44
2000.01.01D00:00:00.000000042
2003.08m
2000.02.14

q)(12h;13 14h)$(42;42 42)
2000.01.01D00:00:00.000000042
(2003.07m;2000.02.12)

Integer

Cast to integer:

q)"i"$10
10i
q)(`int;"i";6h)$10
10 10 10i
q)`int$(neg\)6.1 6.6
6  7
-6 -7

Boolean

Cast to boolean:

q)1h$(neg\)1 0 2
101b
101b

Characters are cast to True.

q)" ",.Q.an
" abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789"
q)"b"$" ",.Q.an
1111111111111111111111111111111111111111111111111111111111111111b

Byte

q)"x"$3 4 5
0x030405
q)"x"$"abc"
0x616263
Casting longs above int infinity

Longs greater than 0wi cast to 0xff

q)"x"$-2 -1 0 1 2+0Wi
0xfdfeffffff

This is considered an error and is planned to change to 0x00.

Temporal

Find parts of time:

q)`hh`uu`ss$03:55:58.11
3 55 58i
q)`year`dd`mm`hh`uu`ss$2015.10.28D03:55:58
2015 28 10 3 55 58i
          | 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 to narrower temporal type truncates rather than rounds

Such conversions use floor, because the day, hour, minute, second… are all [) notions. (What hour are we in; what millisecond are we in…)

For example, "d"$2017.08.23T23:50:12 is 2017.08.23 even though the datetime is closer to 2017.08.24.

As a consequence .z.t-.z.n is typically negative.

Identity

q)("*";0h)$1
1 1

For string values of y, see Tok.

Infinities and beyond

Casting an infinity from a narrower to a wider datatype returns a finite value.

When an integral infinity is cast to an integer of wider type, it is the same underlying bit pattern, reinterpreted.

Since this bit pattern is a legitimate value for the wider type, the cast returns a finite value.

q)`float$0Wh
32767f

The infinity corresponding to numeric x is min 0#x.

Tok
Overloads of $
Q for Mortals §7.2 Cast