math.combinatorics: all-subsets and selections words (contributed by John Benediktsson)

db4
Joe Groff 2010-07-14 09:09:57 -07:00
parent 73833ebb18
commit 37bddfba54
3 changed files with 66 additions and 2 deletions

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@ -103,3 +103,29 @@ HELP: >permutation
{ $notes "For clarification, the following two statements are equivalent:" { $code "10 factoradic >permutation" "{ 1 2 0 0 } >permutation" } }
{ $examples { $example "USING: math.combinatorics.private prettyprint ;" "{ 0 0 0 0 } >permutation ." "{ 0 1 2 3 }" } } ;
HELP: all-subsets
{ $values { "seq" sequence } { "subsets" sequence } }
{ $description
"Returns all the subsets of a sequence."
}
{ $examples
{ $example
"USING: math.combinatorics prettyprint ;"
"{ 1 2 3 } all-subsets ."
"{ { } { 1 } { 2 } { 3 } { 1 2 } { 1 3 } { 2 3 } { 1 2 3 } }"
}
} ;
HELP: selections
{ $values { "seq" sequence } { "n" integer } { "selections" sequence } }
{ $description
"Returns all the ways to take n (possibly the same) items from the "
"sequence of items."
}
{ $examples
{ $example
"USING: math.combinatorics prettyprint ;"
"{ 1 2 } 2 selections ."
"{ { 1 1 } { 1 2 } { 2 1 } { 2 2 } }"
}
} ;

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@ -70,3 +70,20 @@ IN: math.combinatorics.tests
[ { { "a" "b" } { "a" "c" }
{ "a" "d" } { "b" "c" }
{ "b" "d" } { "c" "d" } } ] [ { "a" "b" "c" "d" } 2 all-combinations ] unit-test
[ { { } } ] [ { } all-subsets ] unit-test
[ { { } { 1 } { 2 } { 3 } { 1 2 } { 1 3 } { 2 3 } { 1 2 3 } } ]
[ { 1 2 3 } all-subsets ] unit-test
[ { } ] [ { 1 2 } 0 selections ] unit-test
[ { { 1 2 } } ] [ { 1 2 } 1 selections ] unit-test
[ { { 1 1 } { 1 2 } { 2 1 } { 2 2 } } ]
[ { 1 2 } 2 selections ] unit-test
[ { { 1 1 1 } { 1 1 2 } { 1 2 1 } { 1 2 2 }
{ 2 1 1 } { 2 1 2 } { 2 2 1 } { 2 2 2 } } ]
[ { 1 2 } 3 selections ] unit-test

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@ -1,7 +1,8 @@
! Copyright (c) 2007-2010 Slava Pestov, Doug Coleman, Aaron Schaefer.
! Copyright (c) 2007-2010 Slava Pestov, Doug Coleman, Aaron Schaefer, John Benediktsson.
! See http://factorcode.org/license.txt for BSD license.
USING: accessors assocs binary-search fry kernel locals math math.order
math.ranges namespaces sequences sorting ;
math.ranges namespaces sequences sorting make sequences.deep arrays
combinators ;
IN: math.combinatorics
<PRIVATE
@ -126,3 +127,23 @@ PRIVATE>
: reduce-combinations ( seq k identity quot -- result )
[ -rot ] dip each-combination ; inline
: all-subsets ( seq -- subsets )
dup length [0,b] [
[ dupd all-combinations [ , ] each ] each
] { } make nip ;
: (selections) ( seq n -- selections )
dupd [ dup 1 > ] [
swap pick cartesian-product [
[ [ dup length 1 > [ flatten ] when , ] each ] each
] { } make swap 1 -
] while drop nip ;
: selections ( seq n -- selections )
{
{ 0 [ drop { } ] }
{ 1 [ 1array ] }
[ (selections) ]
} case ;