Question

I’m new to ruby and I’m trying to write a dijkstra function but my hash sort seems doesn’t work at all

def distance(start_code, end_code, map)
#initialize hash for distance 
#distance are initialized to -1
dist_hash=Hash.new()
start_hash=Hash.new()
parent_hash=Hash.new()
close_list=Array.new()
find=-1
map.citylist.each do |e|
  dist_hash[e]=[+1.0/0.0]
end

start_hash[start_code]=0
parent_hash[start_code]=start_code

while (start_hash.empty?)==false


   #sort the hash
  start_hash.sort_by {|k,v| v}
  puts 'value'      
  puts start_hash.values()  
   #pop the first item in the hash
  h=start_hash.shift()
  curr_key=h[0]
  curr_val=h[1]
  curr_city=map.findcity(curr_key)
  close_list<<curr_city.code

   #for every one in adjacent list
  curr_city.get_adj_city().each do |e|


     #if it in the close list then igonore
    if close_list.include?(e)==false  
       #if it is not in the start_hash then add to start hash
      if start_hash.has_key?(e)==false
        dist=map.adj_dist(curr_city.code, e)
        dist=dist+curr_val
        start_hash[e]=dist
        parent_hash[e]=curr_city.code
       #if it is in the start_hash check if we have better distance
      else
        dist=map.adj_dist(curr_city.code, e)
        if (dist+curr_val)<start_hash[e]
          parent_hash[e]=curr_city.code
          start_hash[e]=dist
        end
      end
       #end pf checking single adj city
    end
     #end of check if include in close


  end
   #end of check whole list

  if curr_city.code==end_code
    find=0
    break
  end

end
#end of check node
#result
if find==0
  ptr=end_code
  puts ptr
  puts "final list"

  while ptr!=start_code
    ptr=parent_hash[ptr]
    puts ptr
  end
  return 0
else
  return -1
end

end

When I’m trying to call d.distance(“BUE”, “LOS”, map)

the output looks like

value
0
value
1680
4651
value
10053
8047
4651
value
11094
15839
15839
8047
4651
10779
....

the values are printed out right after hash.sort_by but not sorted. Am I using the method correctly?

Answer 1

the values are printed out right after hash.sort_by but not sorted. Am I using the method correctly?

No. When I’m not sure how something works, I open up IRB and try a few things with it:

hash = {a:1, b:2, c:4, d: 3}
=> {:a=>1, :b=>2, :c=>4, :d=>3}
hash.sort
=> [[:a, 1], [:b, 2], [:c, 4], [:d, 3]]
hash
=> {:a=>1, :b=>2, :c=>4, :d=>3}
hash.sort_by{|k,v| v }
=> [[:a, 1], [:b, 2], [:d, 3], [:c, 4]]
hash
=> {:a=>1, :b=>2, :c=>4, :d=>3}

sort_by does not alter the hash, it returns a result. Try:

hash = hash.sort_by{|k,v| v } # <- don’t use this, it’s an array and you’ll mislead anyone reading this code.

sorted_tuples = hash.sort_by{|k,v| v }

or something like it.