Combination for boolean value array

[Sapna Mishra]

def conditions_combination step_conditions_labels

    conditions_combination_hash = Hash.new

    1.upto(step_conditions_labels.size).flat_map do |n|

      conditions_combination = ""

      step_conditions_labels.permutation(n).map { |condition|  

        if condition.length == n

          conditions_combination += "( "

          condition.each do |condition_label|

            conditions_combination += condition_label+" && "

          end

          conditions_combination = conditions_combination.chomp(' && ')

          conditions_combination += " ) || "

        end

        conditions_combination_hash[n.to_s] = conditions_combination.chomp(' || ').chomp(' && ')   

      } 

    end

    cond = false

    condition_check = conditions_combination_hash[step_conditions_labels.length.to_s]

    if condition_check

      cond = true

    end

    return cond

  end

I have created this function 

conditions_combination_hash = conditions_combination(['true','false','true'])

which gives me different combination like this 

{"1"=>"( true ) || ( false ) || ( true )", "2"=>"( true && false ) || ( true && true ) || ( false && true ) || ( false && true ) || ( true && true ) || ( true && false )", "3"=>"( true && false && true ) || ( true && true && false ) || ( false && true && true ) || ( false && true && true ) || ( true && true && false ) || ( true && false && true )"}

Issue is now I am not able use this combination to check whether it satisfies the condition as it is consider as string class.

[Tales Cione]

You probably could use something like eval. That being said, if you refactor in order to avoid this, it should lead to clearer, safer code

--

Tales.

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[Hassan Schroeder]

On Fri, Feb 22, 2019 at 4:36 AM Sapna Mishra <sapna....@gmail.com> wrote:

> Issue is now I am not able use this combination to check whether it satisfies the condition as it is consider as string class.

If I saw something like that in a PR I would reject it in ~2 seconds.

What actual problem are you trying to solve?

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[Marco Antonio Almeida]

Hi Sapna,

This is a fun exercise to do and also to do some refactoring after I got to understand what you are aiming to do.

First of all, your code is not optimal yet. Let's look at the output of the example you gave:

{"1"=>"( true ) || ( false ) || ( true )", "2"=>"( true && false ) || ( true && true ) || ( false && true ) || ( false && true ) || ( true && true ) || ( true && false )", "3"=>"( true && false && true ) || ( true && true && false ) || ( false && true && true ) || ( false && true && true ) || ( true && true && false ) || ( true && false && true )"}

The combination of 2 and 3 have duplicated information. For example: (true && false && true) are the same as (true && true && false). I have provided a solution for what I understood from your problem below with some comments.

I am considering that you need to solve this in one method, otherwise, I would split in many different methods to make the code more clear. I am also being very cheeky here to introduce many features of the language that would make your life easier and your code much more understandable.

I hope this helps.

# Evaluate the combinations of conditions.

#

# step_conditions_labels - The Array of conditions.

#

# Examples

#

# conditions_combination(%w[true false true])

# # => {1=>true, 2=>true, 3=>false}

#

# conditions_combination(%w[true false true false true])

# # => {1=>true, 2=>true, 3=>true, 4=>false, 5=>false}

#

# Returns a hash of the evaluation of respective combinations.

def conditions_combination(step_conditions_labels)

  # Reduce the Array to the result Hash.

  step_conditions_labels.each_with_index.reduce({}) do |hash, (_, index)|

    # Update each of the Hash keys with the evalutation of the combination.

    hash.update(

      index + 1 =>

        # Eval is the way to go here as Tales mentioned, but it's a very

        # dangerous method. Be careful!

        eval(

          # Array#combination is what does the trick for you. Check it out:

          # https://ruby-doc.org/core-2.6.1/Array.html#method-i-combination

          # The other lines just help on building the condition String.

          step_conditions_labels

            .combination(index + 1)

            .map { |combination| "(#{combination.join(' && ')})" }

            .join(' || ')

        )

    )

  end

end

conditions_combination(%w[true false true])

Best regards,

/ Marco

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[Steve Alex]

I also had a little fund with this. Still not sure what the purpose of the method is but I’m assuming getting the State of an array of booleans. Maybe even, well I don’t know. When I get stuck with what should be a simple combinations of boolean, I go back to ancient methods and draw a picture!  The picture is a Decision Logic Table (DLT) or Truth Table.

Basically if you have an array of N booleans, there are:

 

    2**N combinations

An array with 2 booleans has 2**2 or 4 combinations of 2 variables

  a  yynn

  b  ynyn

An array with 3 booleans has 2**3 or 8 combinations of 3 variables

  a  yyyynnnn

  b  yynnyynn

  c  ynynynyn

An array with 5 booleans has 2**5 or 32 combinations of 5 variables

  a  yyyyyyyyyyyyyyyynnnnnnnnnnnnnnnn

  b  yyyyyyyynnnnnnnnyyyyyyyynnnnnnnn

  c  yyyynnnnyyyynnnnyyyynnnnyyyynnnn

  d  yynnyynnyynnyynnyynnyynnyynnyynn

  e  ynynynynynynynynynynynynynynynyn

Your really don’t want to write and IF statement with 32 combinations! Your example output seemed to be doing some shortcut with OR conditions. Below is a short class I threw together (I did have to go find some old stuff I had written about DLTs [http://stevealex.us/code/2010/08/10/AFOLDS-DAD-DUEL.html]) that return all possible options (not using  OR)

class Truth

  def give_me_the_truth(array)

    # return array of arrays by size of input array

    indexes = array.count

    combos = 2 ** indexes

    truth =  Array.new(indexes,Array.new)

    indexes.times do |v|

      half = (2 ** (indexes - (v-1))/2)

      pick = Array.new(half/2,true)+ Array.new(half/2,false)

      (combos/half).times do |c|

        truth[v] += pick

      end

    end

    truth

  end

  def the_whole_truth(array)

    # returns an array of arrays by size of all possibilites (states?)

    whole = give_me_the_truth(array).transpose

  end

  def nothing_but_the_truth(array)

    # returns the index (state?) of a query

    nothing = the_whole_truth(array).index(array)

  end

end

Truth.new.give_me_the_truth([true,false,true])

=> [[true, true, true, true, false, false, false, false], [true, true, false, false, true, true, false, false], [true, false, true, false, true, false, true, false]]

Gives the possible combination in three arrays (if you need a hash just map it)

Truth.new.the_whole_truth([true,false,true])

=> [[true, true, true], [true, true, false], [true, false, true], [true, false, false], [false, true, true], [false, true, false], [false, false, true], [false, false, false]]

Give the 8 possible conditions as a transposed array.

Truth.new.nothing_but_the_truth([true,false,true])

=> 2

Gives an index into were that array is in the whole truth array.

Not sure if it has any use, 

Steve

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[Sapna Mishra]

Hello Marco,

Thank you for replying to the query with detailed explanation. This is what I wanted to do in my code but the code was not clear but you tried to understand my issue and provided the solution so thanks for that. I was not aware with the combination method before.