Advice requested on array diff

ruby-talk
1

Hi I am new to Ruby and I am working on my first program.

I have two arrays, I want to see the difference between them. I was thinking of ary1 - ary2 but sometimes it should be ary2 - ary1 and I am not sure at run time which one will be different.

So then I thought okay I will check if they are the same and if they are not then I will print both of them out side by side in report fashion.

So in a method I call aryDiffReport I set two variables: count which is the length of the bigger array, and len which is the length of the largest item in either array (for this I wrote my own method *_longestItem - couldn't find anything built in to do it).

Using the two variables and sprintf I construct a third array that looks something like the following when printed out:

one <-> one
two <-> two
   a <-> b
        <-> 12

Okay so my first thoughts is this will be real slow with big arrays.

Being new to Ruby I was thinking I could get some advice on what I am trying to do. Is there a better way? I appreciate all feedback good or bad.

* I kinda thought this was a neat little method so I decided to share:)
def _longestItem(ary1, ary2)
   itemlen = 0
   ary1.each do |i|
     if i.length > itemlen
     then
       itemlen = i.length
     end
   end
   ary2.each do |i|
     if i.length > itemlen
     then
       itemlen = i.length
     end
   end
   return itemlen
end

2

"Dennis Roberts" <dennisr@spacerodent.org> schrieb im Newsbeitrag news:41C54111.5040701@spacerodent.org...

Hi I am new to Ruby and I am working on my first program.

I have two arrays, I want to see the difference between them. I was thinking of ary1 - ary2 but sometimes it should be ary2 - ary1 and I am not sure at run time which one will be different.

So then I thought okay I will check if they are the same and if they are not then I will print both of them out side by side in report fashion.

So in a method I call aryDiffReport I set two variables: count which is the length of the bigger array, and len which is the length of the largest item in either array (for this I wrote my own method *_longestItem - couldn't find anything built in to do it).

Using the two variables and sprintf I construct a third array that looks something like the following when printed out:

one <-> one
two <-> two
  a <-> b
       <-> 12

Okay so my first thoughts is this will be real slow with big arrays.

Being new to Ruby I was thinking I could get some advice on what I am trying to do. Is there a better way? I appreciate all feedback good or bad.

* I kinda thought this was a neat little method so I decided to share:)
def _longestItem(ary1, ary2)
  itemlen = 0
  ary1.each do |i|
    if i.length > itemlen
    then
      itemlen = i.length
    end
  end
  ary2.each do |i|
    if i.length > itemlen
    then
      itemlen = i.length
    end
  end
  return itemlen
end

It's more flexible to calculate maxlen for a single array only. If you want to deal with large arrays gracefully, then this is probably what I'd do:

def max_element_len(enum)
  enum.inject(0) {|max,x|l = x.inspect.length; l > max ? l : max}
end

def array_diff(a1, a2)
  l1, l2 = max_element_len( a1 ), max_element_len( a2 )
  pattern = "%-#{l1}s <-> %-#{l2}s\n"

  a1.zip(a2) {|a,b| printf pattern, a.inspect, b.inspect }

  for i in a1.length ... a2.length
    printf pattern, "nil", a2[i].inspect
  end
end

array_diff %w{a bbb c}, %w{a bbb c}

"a" <-> "a"
"bbb" <-> "bbb"
"c" <-> "c"
=> 3...3

array_diff %w{a bbb c}, %w{a bbb c dd}

"a" <-> "a"
"bbb" <-> "bbb"
"c" <-> "c"
nil <-> "dd"
=> 3...4

array_diff %w{a bbb c dd}, %w{a bbb c}

"a" <-> "a"
"bbb" <-> "bbb"
"c" <-> "c"
"dd" <-> nil
=> 4...3

Kind regards

    robert