Nonrandom random command line replacement in Perl

Question

What's a good, concise way to avoid sequential random value which are close? e.g., using rand in perl, but assuring a minimum 0.2x difference/distribution between any sequential values? I've tried a few ideas like re-sampling rand if the values are close, but then I need a script, and I don't know how to do this cleanly in a one-liner.

The context is that I'm doing a search-replace using the commandline with perl. The idea is that in each line, a string is replaced with a random value from an array.

echo ":z:z:z:" | tr ':' '\n' | perl -pe '@numbers=(1.2, 3.4, 5.6, 7.8); $number = $numbers[rand @numbers];  s/z/" : ".( $number )/ge'

The output is something like this:

: 3.4
: 5.6
: 5.6
: 1.2

See how the 5.6 repeats? I want to avoid that. In my use-case, the @numbers array contains ~100 elements. I want to adjust rand @numbers so that the selected array values are further apart.

Related: [How can I take n elements at random from a Perl array?](http://stackoverflow.com/q/8963228) — ThisSuitIsBlackNot, Mar 10 '17 at 18:12
Will there always be fewer lines of input than numbers in your array? — ThisSuitIsBlackNot, Mar 10 '17 at 18:15
keep track of the previous value, and if you get a new value too close, retry the rand? — ysth, Mar 10 '17 at 18:41
Thanks for the question, and sorry for the slow reply. There will be vastly more lines of input than the size of the array. i.e. array elements will be reused. Moreover, I'm interested in avoiding nearby elements, not just repeats. — Albert Jones, Mar 10 '17 at 22:37
Imagine the array was 100 numbers, 1..100. I don't want two consecutive random numbers to be within 20 of each other. — Albert Jones, Mar 11 '17 at 04:37

score 1 · Answer 1 · answered Mar 10 '17 at 18:23

1

If you're sure there will always be fewer lines of input than array elements, you can shuffle the array once at the beginning and then remove a single element for every line:

$ echo -e 'foo\nbar\nbaz' | \
    perl -MList::Util=shuffle -lpe'
        BEGIN { @numbers = shuffle map { 1.2 * $_ } 1..4 }
        $_ = pop @numbers
    '
2.4
4.8
3.6

answered Mar 10 '17 at 18:23

ThisSuitIsBlackNot

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Thanks for this, and it's a valid assumption, but in fact, Ill have much more input than items in the array. – Albert Jones Mar 10 '17 at 22:38

Nonrandom random command line replacement in Perl

1 Answers1