From: Joe Buck <semle2000@...>
Date: 2010-01-02T05:00:30+09:00
Subject: Re: Delete elements in array, break, and keep changes?

Alright, I won't hide you from the details. I have a map (google maps 
API) with data points (100,000+).

I'm doing server side clustering of the points to limit the amount of 
data I send to the client (I'm using the Ruby On Rails framework).

I start out with an array of 100,000 spots. Each spot is a hash with a 
:lat and :lng. I need to iterate through the array and group the spots 
into clusters. I break the world up into 30/30 degree clusters, so I 
have 72 clusters to put the spots in.

The spots are ordered by longitude.

Here is the code (do you use code snippet tags here?). Note that 
'listings' is the array of spots ordered by longitude.

#---------------------------------------------------------------------
  for i in (0..72)

    # Move to the next block.
    bNextRow = (i%nRows == 0 && i!=0)
    cLatLngBox.topRightLat = bNextRow ? 90 : cLatLngBox.topRightLat-size
    cLatLngBox.topRightLng = bNextRow ? (cLatLngBox.topRightLng+size) : 
cLatLngBox.topRightLng
    cLatLngBox.botLeftLat = bNextRow ? 90-size : 
(cLatLngBox.botLeftLat-size)
    cLatLngBox.botLeftLng = bNextRow ? (cLatLngBox.botLeftLng+size) : 
cLatLngBox.botLeftLng

    # Holds the index of each spot we added to a cluster. We will remove 
these
    # from the listing when done.
    cRemove = []

    # Our new cluster.
    cluster = {:lat=>0, :lng=>0, :size=>0}

    # Iterate through all the spots, adding them to clusters.
    listings.each_with_index do |listing, h|
      if cLatLngBox.is_in_box?(listing[:lat], listing[:lng])

        # Add to the cluster.
        cluster[:size]+=1
        cluster[:lat]+=listing[:lat].to_f
        cluster[:lng]+=listing[:lng].to_f

        # Tag the spot for removal.
        cRemove << h
      else
        # We cheat here. Because the spots are ordered by longitude 
(-180 to 180) we'll check
        # if the spot longitude exceeds our current max. If it does 
we're done with this loop.
        if listing[:lng].to_f > cLatLngBox.topRightLng
          break
        end
      end
    end

    # Remove all the items that were clustered.
    cRemove.each do |index|
      listings.delete_at(index)
    end
#---------------------------------------------------------------------

This is faster than not removing the items. But I'd like to remove them 
while I'm in the above loop, but still have the ability to break.
-- 
Posted via http://www.ruby-forum.com/.