What is the best way to handle this type of inclusive logic in Ruby? - ruby

Question

Is there a better way of handling this in Ruby, while continuing to use the symbols?
pos = :pos1 # can be :pos2, :pos3, etc.
if pos == :pos1 || pos == :pos2 || pos == :pos3
puts 'a'
end
if pos == :pos1 || pos == :pos2
puts 'b'
end
if pos == :pos1
puts 'c'
end
The obvious way would be swapping out the symbols for number constants, but that's not an option.
pos = 3
if pos >= 1
puts 'a'
end
if pos >= 2
puts 'b'
end
if pos >= 3
puts 'c'
end
Thanks.
EDIT
I just figured out that Ruby orders symbols in alpha/num order. This works perfectly.
pos = :pos2 # can be :pos2, :pos3, etc.
if pos >= :pos1
puts 'a'
end
if pos >= :pos2
puts 'b'
end
if pos >= :pos3
puts 'c'
end

Answer 1

Not sure if this is the best way......
I would make use of the include? method from array:
puts 'a' if [:pos1, :pos2, :pos3].include? pos
puts 'b' if [:pos1, :pos2].include? pos
puts 'c' if [:pos1].include? pos

Answer 2

Just use the case statement
pos = :pos1 # can be :pos2, :pos3, etc.
case pos
when :pos1 then %w[a b c]
when :pos2 then %w[a b]
when :pos3 then %w[a]
end.each {|x| puts x }

Answer 3

There are lots of different ways to get your output. Which one you
want depends on your specific objections to your if statements.
I've added a bunch of extra formatting to make the output easier
to read.
If you don't like the logical ORs and how they separate the results
from the output, you can use a lookup table:
puts "Lookup table 1:"
lookup_table1 = {
:pos1 => %w{a b c},
:pos2 => %w{a b },
:pos3 => %w{a },
}
[:pos1, :pos2, :pos3].each { |which|
puts "\t#{which}"
lookup_table1[which].each { |x| puts "\t\t#{x}" }
}
Or, if you want all the "work" in the lookup table:
puts "Lookup table 2:"
lookup_table2 = {
:pos1 => lambda do %w{a b c}.each { |x| puts "\t\t#{x}" } end,
:pos2 => lambda do %w{a b }.each { |x| puts "\t\t#{x}" } end,
:pos3 => lambda do %w{a }.each { |x| puts "\t\t#{x}" } end,
}
[:pos1, :pos2, :pos3].each { |which|
puts "\t#{which}"
lookup_table2[which].call
}
If your problem is that symbols aren't ordinals, then you can
ordinalize them by converting them to strings:
puts "Ordinals by .to_s and <="
[:pos1, :pos2, :pos3].each { |which|
puts "\t#{which}"
if which.to_s <= :pos3.to_s
puts "\t\ta"
end
if which.to_s <= :pos2.to_s
puts "\t\tb"
end
if which.to_s <= :pos1.to_s
puts "\t\tc"
end
}
Or you could monkey patch a comparison operator into the Symbol
class (not recommended):
puts "Ordinals by Symbol#<="
class Symbol
def <= (x)
self.to_s <= x.to_s
end
end
[:pos1, :pos2, :pos3].each { |which|
puts "\t#{which}"
if which <= :pos3
puts "\t\ta"
end
if which <= :pos2
puts "\t\tb"
end
if which <= :pos1
puts "\t\tc"
end
}
Or you could use a lookup table to supply your ordinal values:
puts "Ordinals through a lookup table:"
ordinal = {
:pos1 => 1,
:pos2 => 2,
:pos3 => 3,
}
[:pos1, :pos2, :pos3].each { |which|
puts "\t#{which}"
if ordinal[which] <= 3
puts "\t\ta"
end
if ordinal[which] <= 2
puts "\t\tb"
end
if ordinal[which] <= 1
puts "\t\tc"
end
}
Those are the obvious ones off the top of my head. It is hard to say what would be best without more specifics on what your problem with your if approach is; your second example indicates that what you really want is a way to make symbols into ordinals.

Answer 4

More generically, you can use this:
pos = :pos3
arr = [:pos1,:pos2,:pos3]
curr = 'a'
idx = arr.length
while idx > 0
puts curr if arr.last(idx).include? pos
curr = curr.next
idx -= 1
end
Or this, for your specific example:
puts 'a'
puts 'b' if pos != :pos3
puts 'c' if pos == :pos1