$ 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 interprets the value from a string, 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

Use the following symbols to extract parts of a temporal type:

• year to provide year as an integer
• month to provide month datatype
• mm to provide month as an integer, where January is 01i
• week to provide a date datatype, presenting the week in which the temporal variable resides. The value returned is the start of the week (Monday). If the date represents a Monday, it is not altered.
• dd to provide day as an integer, where 1st of the month is 1i
• hh to provide hour as an integer
• uu to provide minutes as an integer
• ss to provide seconds as an integer

For example:

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

The following shows which information can be extracted from each temporal datatype.

          | 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

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.

Numeric calculations on the base numeric type can also be used to extract part of a temporal type, for the example using the mod keyword:

milliseconds: "i"$01:00:00.100 mod 1000                         / extract milliseconds from time datatype
milliseconds: "i"$mod[;1000]"t"$2000.01.01T12:00:00.500         / extract milliseconds from datetime datatype
nanoseconds: "i"$2014.11.22D17:43:40.123456789 mod 1000000000   / extract nanoseconds from timestamp datatype

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.

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Tok

Overloads of $

Q for Mortals §7.2 Cast