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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:

1	proc test {} {
2	proc randlist {a b} { return [expr {int(rand()*2) ? -1 : 1}] }
3	proc repeat { what {times 1}} {
4	for {set a 0} {$a < $times} {incr a} {
5	uplevel 1 $what
6	}
7	}
8	puts "num prob. to be found in list at that place:"
9	puts "x 1 2 3 4 5 6 7 8 9 0"
10	for {set i 0} { $i <= 9 } {incr i} {
11	set prob [list $i]
12	for {set j 0} { $j <= 9} { incr j} {
13	set k 0
14	repeat {if {[lsearch [lsort -command randlist [list 1 2 3 4 5 6 7 8 9 0]] $i] == $j} { incr k }} 1000
15	lappend prob [expr {($k*100)/1000}]
16	}
17	puts [join $prob " "]
18	}
19	}

Running this gives us:

1	num prob. to be found in list at that place:
2	x 1 2 3 4 5 6 7 8 9 0
3	0 24 25 19 12 6 5 1 1 1 1
4	1 5 6 7 8 11 11 10 12 13 11
5	2 5 5 8 9 10 13 11 11 10 11
6	3 6 4 7 9 9 11 12 11 13 11
7	4 5 6 8 7 10 11 11 11 10 13
8	5 7 6 6 9 11 10 10 11 11 12
9	6 5 5 8 9 12 10 10 11 12 12
10	7 5 7 8 7 10 11 10 12 12 13
11	8 6 5 8 7 12 11 10 12 12 13
12	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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1	proc randomizelist {list} {
2	set l [llength $list]
3	for {set i 0} {$i<=$l} {incr i} {
4	set x [lindex $list [set p [expr {int(rand()*$l)}]]]
5	set list [lreplace $list $p $p]
6	set list [linsert $list [expr {int(rand()*$l)}] $x]
7	}
8	return $list
9	}

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	set word "theword"
2	set tmp "[join [randomizelist [split $word {}]] {}]"
3	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:

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

Michael

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