Generate random number within specified range without REDUNDANCY in TCL - random

Question

hi I need to generate 30 random numbers without any repeatations of numbers in TCL.
Here is the code to generate random number which works fine, but will generate redundant numbers.
proc myRand { min max } {
set maxFactor [expr [expr $max + 1] - $min]
set value [expr int([expr rand() * 100])]
set value [expr [expr $value % $maxFactor] + $min]
return $value
}
for {set i 1} {$i < 31} {incr i} {
upvar 0 fnode($i) fnod($i)
set fnod($i) [myRand 1 20] ;# random number is generated between 1 to 20
}
Anyone please help out.

Answer 1

To generate a list of random numbers without repetitions, you've got to put in code to explicitly prevent them. In general, random sequences most certainly can contain repetitions, just as if you toss a coin, it will sometimes come up heads twice (or more) in a row.
set r -1; # Some value that definitely isn't in the sequence
for {set i 1} {$i < 31} {incr i} {
upvar 0 fnode($i) fnod($i)
while {$r == [set r [myRand 1 20]]} {
# Empty body
}
set fnod($i) $r; # Random number is generated between 1 to 20
}
Note that if you're picking 30 values from a collection of 20 numbers, you'll necessarily (by the pigeonhole principle) get some repetitions. But we can prevent values from occurring twice in a row.
Your random number generator is slightly horrifying too. This is the idiomatic version:
proc myRand {min max} {
set range [expr {$max - $min + 1}]
return [expr {$min + int(rand() * $range)}]
}

Answer 2

Code to generate a sequence of unique random numbers could be written like this, but it won't work unless $nnums is less than or equal to $rmax.
set nnums 30
set rmax 20
set nums {}
if {$nnums > $rmax} {
puts "You can't get $nnums unique values from a range of 1 to $rmax!"
} else {
while {[llength $nums] < $nnums} {
set n [myRand 1 $rmax]
if {$n ni $nums} {lappend nums $n}
}
set nums [linsert $nums 0 {}]
for {set i 1} {$i <= $nnums} {incr i} {
set fnod($i) [lindex $nums $i]
}
}
(When I started writing this answer, I was to preoccupied to notice that you were trying to get 30 unique numbers from a 1-20 range, which is impossible, as others have pointed out.)
There are some other problems with your code. You don't need to do nested calls to expr:
expr [expr $max + 1] - $min
# is the same as
expr {$max + 1 - $min}
so your random number generator can be written like this:
proc myRand {min max} {
expr {int(rand() * 100) % ($max + 1 - $min) + $min}
}
but that is still more calculations than necessary. This version is better:
proc myRand {min max} {
expr {int(rand() * ($max + 1 - $min)) + $min}
}
You can also use this:
package require math
::math::random 1 21
(Note 21, not 20!)