100 lines
3.5 KiB
Factor
100 lines
3.5 KiB
Factor
! :folding=indent:collapseFolds=0:
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! $Id$
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!
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! Copyright (C) 2003, 2004 Slava Pestov.
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!
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! Redistribution and use in source and binary forms, with or without
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! modification, are permitted provided that the following conditions are met:
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!
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! 1. Redistributions of source code must retain the above copyright notice,
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! this list of conditions and the following disclaimer.
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!
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! 2. Redistributions in binary form must reproduce the above copyright notice,
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! this list of conditions and the following disclaimer in the documentation
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! and/or other materials provided with the distribution.
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!
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! THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
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! INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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! FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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! DEVELOPERS AND CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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! SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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! PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
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! OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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! WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
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! OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
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! ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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IN: random
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USE: arithmetic
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USE: combinators
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USE: kernel
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USE: lists
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USE: stack
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: random-digit ( -- digit )
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0 9 random-int ;
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: random-symmetric-int ( max -- random )
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#! Return a random integer between -max and max.
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dup neg swap random-int ;
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: chance ( n -- boolean )
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#! Returns true with a 1/n probability, false with a (n-1)/n
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#! probability.
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1 swap random-int 1 = ;
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: random-element ( list -- random )
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#! Returns a random element from the given list.
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dup >r length pred 0 swap random-int r> nth ;
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: random-subset ( list -- list )
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#! Returns a random subset of the given list. Each item is
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#! chosen with a 50%
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#! probability.
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[ drop random-boolean ] subset ;
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: car+ ( list -- sum )
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#! Adds the car of each element of the given list.
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0 swap [ car + ] each ;
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: random-probability ( list -- sum )
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#! Adds the car of each element of the given list, and
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#! returns a random number between 1 and this sum.
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1 swap car+ random-int ;
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: random-element-iter ( list index -- elem )
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#! Used by random-element*. Do not call directly.
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[ unswons unswons ] dip ( list elem probability index )
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swap - ( list elem index )
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dup 0 <= [
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drop nip
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] [
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nip random-element-iter
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] ifte ;
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: random-element* ( list -- elem )
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#! Returns a random element of the given list of comma
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#! pairs. The car of each pair is a probability, the cdr is
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#! the item itself. Only the cdr of the comma pair is
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#! returned.
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dup 1 swap car+ random-int random-element-iter ;
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: random-subset* ( list -- list )
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#! Returns a random subset of the given list of comma pairs.
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#! The car of each pair is a probability, the cdr is the
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#! item itself. Only the cdr of the comma pair is returned.
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dup [ [ [ ] ] dip car+ ] dip ( [ ] probabilitySum list )
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[
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[ 1 over random-int ] dip ( [ ] probabilitySum probability elem )
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uncons ( [ ] probabilitySum probability elema elemd )
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-rot ( [ ] probabilitySum elemd probability elema )
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> ( [ ] probabilitySum elemd boolean )
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[
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drop
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] [
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-rot ( elemd [ ] probabilitySum )
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[ cons ] dip ( [ elemd ] probabilitySum )
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] ifte
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] each drop ;
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