[code] Split a long pathstring ~in half at the nearest '/'

[Dan Rathbun]

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[ code ] Split a long pathstring ~in half at the nearest '/'

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Scenario:
(a) You have a very long absolute pathstring, and you want to display it in a UI.messagebox, but don't want the dialog to be tremendously wide (or definately not wider than the screen.)
(b) You want the pathstring to look "correct", having the split on the nearest '/' near the middle of the string.

Question: The following code is what I came up with (as I could not find any built-in Enumerable iterator that would do what I wanted.) Can anyone suggest a better or more consise (more readable,) way of doing this?

So you would have code that needs the method, like:

Code: Select all

info = "Couldn't load:\n\n"
info<< path_knife(pathstring)
info<< "\n\nAnswer this question for some action?"
choice = UI.messagebox( info, MB_YESNO|96 )
choice == IDYES ? do_sometask() : do_othertask


And the path_knife() method:

Code: Select all

def path_knife(path,max=60)
  path = File.expand_path(path)
  if path.length > max
    # cut the file path into 2 lines
    spa = [0.54,0.58,0.62,0.66,0.71]
    i= for e in spa
      c = ((path.length)*e).to_i
      x = while c >= 0
        (path[c,1]=='/')?(break c):((c==0)?(break 0):(c = c-1))
      end # while
      (x.to_f/(path.length.to_f-1.0) >= 0.45)?(break x):((e==spa.last)?(break 0):(next))
    end # for
    #    
    return "#{path[0,i+1]}    \n#{path[i+1,path.length-1]}    " if i>0
    return "#{path}    " # just in case i is still 0
  else # leave it as one line
    return "#{path}    "
  end
end # def
 

Here's an "unwound" edition of the same method, with annotation comments:

Code: Select all

def path_knife(path,max=60)
  path = File.expand_path(path)
  if path.length > max
    # cut the file path into 2 lines
    
    # start point array of %
    spa = [0.54,0.58,0.62,0.66,0.71]
    i= for e in spa
      # Get a start index at e% into path.
      c = ((path.length)*e).to_i
      
      # Iterate backwards from startpoint
      # until a '/' character is found, or
      # 0 is reached. Return result in x.
      x = while c >= 0
        if (path[c,1]=='/')
          break c
        else
          if c==0
            break 0
          else
            c = c-1
          end
        end
      end # while
      
      # Test x to see if it's at least 45% of path;
      # if so, return result in i. If not, next.
      if x.to_f/(path.length.to_f-1.0) >= 0.45
        break x
      else
        break 0 if e==spa.last
      end
    end # for
    #
    return "#{path[0,i+1]}    \n#{path[i+1,path.length-1]}    " if i>0
    return "#{path}    " # just in case i is still 0
  else # leave it as one line
    return "#{path}    "
  end
end # def
 

[Dan Rathbun]

This is what a dialog using path_knife() looks like:

path_knife.png

[todd burch]

Code: Select all

def path_knife(path,max=60)
   path = File.expand_path(path)
   if path.length > max
      s = []
      minlen = path.length
      path.gsub(/\//) {|piece|
         len = ($`.length - $'.length).abs
         if len < minlen then
            s = [ $`, $']
            minlen = len
         end
      }   
      return "#{s[0]}/\n#{s[1]}"
   else # leave it as one line
      return "#{path}"
   end
end # def
 
puts path_knife("C:/Program Files/Google/Google SketchUp 8/Plugins/test/error/NoMemoryError.rb")

[david.]

How about:

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def path_knife( path, max=60 )
    fpath = File.expand_path(path)

    if( fpath.length > max )
        rMax = fpath[0..max].reverse =~ /\//
        "#{fpath[0..(max - rMax)]}\n\t#{fpath[(max + 1 - rMax)...fpath.length]}"
    else
        "#{fpath}"
    end
end


[todd burch]

Looks good david, but it doesn't satisfy

(b) You want the pathstring to look "correct", having the split on the nearest '/' near the middle of the string.

[Dan Rathbun]

Isn't this a 'vicious' little Ruby exercise ??

At first blush, you think, "Oh simple string manipulation. No problem.." Then you actually try and code it.

It's a good one for a Ruby class, for sure.


@Todd: I had forgotten about the $` (prematch) and $' (postmatch) globals. That could simplify things, especially the string output at the end as you showed.

@Dave: I had entertained the idea of dup'ing and reversing the path, and then using the standard String class iterator .each_byte and then stoping when a '/' was found between 45%..55% of the path length. I just didn't want to figure out that night, how to invert the reverse index.

[david.]

Well, I am using "max" to determine about where to split the path string. The assumption being that you know what string length looks OK in general. That should be a valid assumption for most legitimate path strings (at least, it would be for any system I've ever encountered). If strings get much longer than that, you'll need a slightly modified version to split into more than 2 lines. The code I provided could easily be modified to take fpath.length/2 to approximate the middle of the path string on the fly. Or, it could easily be modified to do splits into more than 2 lines.

[TIG]

Why not ?

Code: Select all

def path_knife(path, max=60)
  return path if path.length<=max
  return path[0..(max/2).to_i]+"..."+path[-(max/2).to_i/2..-1]
end#def   

[Dan Rathbun]

Why not ?

Code: Select all

def path_knife(path, max=60)
  return path if path.length<=max
  return path[0..(max/2).to_i]+"..."+path[-(max/2).to_i/2..-1]
end#def        

That does not meet the specifications. It will divide folder names.
(The instructor grades you a C- for your effort.)

EDIT: .. AND it does not return a two line string (or add padding to which is lacking in the API implementation of the UI.messagbox method.)

EDIT2: Tested your suggestion and for the test path, it returns:
"C:/Program Files/Google/Google ...oMemoryError.rb"
So, it also chops off part the filename at the end.

[Dan Rathbun]

Ok here's my current version:

Code: Select all

def self.path_knife(path,max=60)
  # make sure it's a Ruby path using '/'.
  path = File.expand_path(path)
  if path.length > max
    # cut the file path into 2 lines
    ok = ((path.length-1)*0.45).to_i
    cut = path.split(//).each_with_index { |e,i|
      break i if( e=='/' && i>=ok )
    }
    cut = 0 unless cut.is_a?(Integer)
    return "  #{path[0..cut]}   \n  #{path[(cut+1)..-1]}   " if cut>0
  end
  # otherwise, leave it as one line
  return "  #{path}   "
  #
end # def
 

EDIT: Added test after iterator, to set cut to 0, if a string had no '/' characters (in which case each_with_index just returns the array characters.)
Also removed frivolous line before iterator: cut = 0

EDIT 2:(2011-02-19) Simplified path substring references (line 11.)
Removed frivolous else clause (were lines 12 and 13.)