? Roll, Deal, Permute
Random selections, with or without duplicates
Roll and Deal
A list of random selections.
x?y ?[x;y] / Roll
neg[x]?y ?[neg[x];y] / Deal
Where x is an int atom, returns a list of x randomly selected items, without duplication if x is negative.
Where y is
-
a list, the result items are items of
yq)5?`Arthur`Steve`Dennis `Arthur`Arthur`Steve`Dennis`Arthur q)2?("a";0101b;`abc;`the`quick;2012.06m) `abc 2012.06m q)-3?`the`quick`brown`fox `brown`quick`fox -
an atom, the result items have the same type as
yand are generated as followsy range operator ---------------------------------------------------------------- integer til y Roll, Deal 0Ng GUIDs Roll, Deal float, temporal 0 to y Roll 0i ints Roll 0 longs Roll 0b 01b Roll " " .Q.a Roll 0x0 bytes Roll numeric symbol `n symbols, each of n chars (n≤8) Roll from abcdefghijklmnop
q)10?5 / roll 10 (5-sided dice)
4 2 1 1 3 2 0 0 2 2
q)-5?20 / deal 5
13 11 8 12 19
q)-10?10 / first 10 ints in random order
9 3 5 7 2 0 6 1 4 8
q)(asc -10?10)~asc -10?10
1b
q)-1?0Ng / deal 1 GUID
,fd2db048-decb-0008-0176-01714e5eeced
q)count distinct -1000?0Ng / deal 1000 GUIDs
1000
q)5?4.5 / roll floats
3.13239 1.699364 2.898484 1.334554 3.085937
q)4?2012.09m / roll months
2006.02 2007.07 2007.07 2008.06m
q)30?" "
"tusrgoufcetphltnkegcflrunpornt"
q)16?0x0 / roll 16 bytes
0x8c6b8b64681560840a3e178401251b68
q)20?0b / roll booleans
00000110010101000100b
q)10?`3 / roll short symbols
`bon`dec`nei`jem`pgm`kei`lpn`bjh`flj`npo
q)rand `6
`nemoad
Deal of GUID uses a mix of process ID, current time and IP address to generate the GUID, and successive calls may not allow enough time for the current time reading to change.
q)count distinct {-1?0ng}each til 10
5
Permute
0N?x
Where x is
- a non-negative int atom, returns the items of
til xin random order - a list, returns the items of
xin random order
(Since V3.3.)
q)0N?10 / permute til 10
8 2 4 1 6 0 5 3 7 9
q)0N?5 4 2 / permute items
4 5 2
q)0N?"abc" / permute items
"bac"
q)0N?("the";1 2 4;`ibm`goog) / permute items
`ibm`goog
1 2 4
"the"
Seed
Deal, Roll, Permute and rand use a constant seed on kdb+ startup: scripts using them can be repeated with the same results. You can see and set the value of the seed with system command \S.)
To use GUIDs as identifiers, use Deal, not Roll.
$ q
..
q)1?0Ng / roll 1 GUID
,8c6b8b64-6815-6084-0a3e-178401251b68
q)\\
$ q
..
q)1?0Ng / roll 1 GUID
,8c6b8b64-6815-6084-0a3e-178401251b68
q)\\
$ q
..
q)-1?0Ng / deal 1 GUID
,2afe0040-2a1b-bfce-ef3e-7160260cf992
q)\\
$ q
..
q)-1?0Ng / deal 1 GUID
,753a8739-aa6b-3cb4-2e31-0fcdf20fd2f0
Roll uses the current seed (\S 0N). Deal uses a seed based on process properties and the current time. This means -10?0Ng is different from {first -1?0Ng}each til 10.
Errors
| error | cause |
|---|---|
| length | neg x exceeds count y |
| type | x is negative (Roll only) |