Srinivas Jonnalagadda
1/16/2006 5:12:00 AM
Dear all,
I have a requirement as below.
There are 'n' containers of lengths {l_i}, i = 1,..,n. All these
containers are collected into an array. Picking one element at a time
from each container, an array has to be constructed and either yielded
or accumulated.
I have written the following code that seems to work reasonably. Are
there simpler or more efficient ways of doing this?
Thanks in advance,
JS
* * * *
def generate_combinations(cont_ary, &blk)
cont_count = cont_ary.length
return if cont_count < 1
if cont_count == 1
if block_given?
cont_ary[0].each { | el | yield [el] }
return
else
return cont_ary[0].collect { | el | [el] }
end
end
cur_indices = Array.new(cont_count, 0)
combinations = []
generate_combinations_iterator(cont_ary, 0, cur_indices,
:working_set => Array.new(cont_count),
:accumulator => combinations,
&blk)
return combinations unless block_given?
end
#
def generate_combinations_iterator(cont_ary, cur_cont, cur_indices, opts
= {}, &blk)
cont_ary[cur_cont].each_with_index do | el, i |
opts[:working_set][cur_cont] = el
case cur_cont
when 0
cur_indices[cur_cont] = i
(1...cur_indices.length).each { | j | cur_indices[j] = 0 }
generate_combinations_iterator(cont_ary, cur_cont + 1,
cur_indices, opts, &blk)
when cont_ary.length-1
if block_given?
yield opts[:working_set]
else
opts[:accumulator] << Array.new(opts[:working_set])
end
else
cur_indices[cur_cont] = i
generate_combinations_iterator(cont_ary, cur_cont + 1,
cur_indices, opts, &blk)
end
end
end
#
Output
------
irb(main):011:0> load 'combination-generator.rb'
=> true
irb(main):012:0> ary1 = []
=> []
irb(main):013:0> generate_combinations(ary1)
=> nil
irb(main):014:0> ary2 = [[1, 2, 3, 4]]
=> [[1, 2, 3, 4]]
irb(main):015:0> pp generate_combinations(ary2)
[[1], [2], [3], [4]]
=> nil
irb(main):016:0> ary3 = [[1, 2, 3, 4], ['a', 'b', 'c']]
=> [[1, 2, 3, 4], ["a", "b", "c"]]
irb(main):017:0> pp generate_combinations(ary3)
[[1, "a"],
[1, "b"],
[1, "c"],
[2, "a"],
[2, "b"],
[2, "c"],
[3, "a"],
[3, "b"],
[3, "c"],
[4, "a"],
[4, "b"],
[4, "c"]]
=> nil