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[TCL] Randomize List

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CyBex

03-11-2006, 00:00

| [TCL] Randomize List

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nie da
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1	proc randlist {a b} { return [expr {int(rand()*2) ? -1 : 1}] }

lsort -command randlist [list a b c d e]
lsort -command randlist [chanlist #tcl]

mfG CyBex @ QuakeNet, UnderNet, EFNet, Freenode, euIRC, GameSurge & ShadowWorld - Files

Gotisch

03-19-2006, 19:49

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Imho this doesn't really randomize a list. I wrote this proc to check how big the probability is to find a entry at a certain position of the list:

proc test {} {
    proc randlist {a b} { return [expr {int(rand()*2) ? -1 : 1}] }
    proc repeat { what {times 1}} {
        for {set a 0} {$a < $times} {incr a} {
            uplevel 1 $what
        }
    }
    puts "num    prob. to be found in list at that place:"
    puts "x    1    2    3    4    5    6    7    8    9    0"
    for {set i 0} { $i <= 9 } {incr i} {
        set prob [list $i]
        for {set j 0} { $j <= 9} { incr j} {
            set k 0
            repeat {if {[lsearch [lsort -command randlist [list 1 2 3 4 5 6 7 8 9 0]] $i] == $j} { incr k }} 1000
            lappend prob [expr {($k*100)/1000}]
        }
        puts [join $prob "    "]
    }
}

Running this gives us:

num     prob. to be found in list at that place:
x       1       2       3       4       5       6       7       8       9       0
0       24      25      19      12      6       5       1       1       1       1
1       5       6       7       8       11      11      10      12      13      11
2       5       5       8       9       10      13      11      11      10      11
3       6       4       7       9       9       11      12      11      13      11
4       5       6       8       7       10      11      11      11      10      13
5       7       6       6       9       11      10      10      11      11      12
6       5       5       8       9       12      10      10      11      12      12
7       5       7       8       7       10      11      10      12      12      13
8       6       5       8       7       12      11      10      12      12      13
9       22      23      18      12      8       3       3       1       0       0

This means that the number 0 (last entry in list) has a probability to be in the first position of the list after the "randomisation" of 24%. On a perfect shuffle this should be 10% (100/(entries in list))
This "gap" gets smaller with more entries ( with 15 entries its barely noticable) but worse with less (with 5 entries the last entry has a prob of 50% to be first after the shuffle)

Or am i calculating it wrong?

for a more in dept discussion about shuffleling a list: http://wiki.tcl.tk/941

CyBex

03-20-2006, 20:25

| [TCL] Randomize List (2nd)

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proc randomizelist {list} {
    set l [llength $list]
    for {set i 0} {$i<=$l} {incr i} {
        set x [lindex $list [set p [expr {int(rand()*$l)}]]]
        set list [lreplace $list $p $p]
        set list [linsert $list [expr {int(rand()*$l)}] $x]
    }
    return $list
}

A 2nd try

mfG CyBex @ QuakeNet, UnderNet, EFNet, Freenode, euIRC, GameSurge & ShadowWorld - Files

BouBBIN

04-21-2006, 08:47

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to randomize a single word with that proc use:

1
2
3

set word "theword"
set tmp "[join [randomizelist [split $word {}]] {}]"
return $tmp"

Wherever you go, there you are.

schlenk

07-06-2006, 16:49

Member since 07/2006
3 Posts

If you don't care for speed:

package require struct::list ;# from tcllib
set list {a b c d}
set perms [struct::list permutations $list] ;# get all permutations
set randlist [lindex $perms [expr {int(rand()*[llength $perms]}] ;# pick one at random

Michael

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