How store/count individual cluster sizes and plot

I have a model that generates clusters of yellow patches and I am interested in looking at the frequency distribution of cluster sizes. To do this I have co-opted the code from 'Patch Clusters Example' in the Code Library of NetLogo. It seems to be working (see photos below) in terms of finding the clusters (although I would prefer that it did not count green patches in the clusters), but I can't figure out how to get the sizes (or patch counts) of each of these clusters. Ideally I would like to make a histogram of the frequency distribution of cluster sizes (excluding green patches) and be able to export that data.

Furthermore, it would be great if I could figure out a way to get the histogram of cluster size frequencies while the model is running.

The code I am using to get the clusters is right out of 'Patch Clusters Example' except I kill all the agents so I can read the numbers. Here it is...

to find-clusters
ask turtles [die] ;; this clears the board so I can see the clusters
  loop [
    ;; pick a random patch that isn't in a cluster yet
    let seed one-of patches with [(cluster = nobody)]
    ;; if we can't find one, then we're done!
    if seed = nobody
    [ show-clusters
      stop ]
    ;; otherwise, make the patch the "leader" of a new cluster
    ;; by assigning itself to its own cluster, then call
    ;; grow-cluster to find the rest of the cluster
    ask seed
    [ set cluster self
      grow-cluster ]
  ]
end


to grow-cluster  ;; patch procedure
  ask neighbors with [(cluster = nobody) and
    (pcolor = [pcolor] of myself )]
  [ set cluster [cluster] of myself
    grow-cluster ]
end

;; once all the clusters have been found, this is called
;; to put numeric labels on them so the user can see
;; that the clusters were identified correctly
to show-clusters
  let counter 0
  loop
  [ ;; pick a random patch we haven't labeled yet
    let p one-of patches with [plabel = ""]
    if p = nobody
      [ stop ]
    ;; give all patches in the chosen patch's cluster
    ;; the same label
    ask p
    [ ask patches with [cluster = [cluster] of myself]
      [ set plabel counter] ]
    set counter counter + 1 ]

end

Thanks for your help!

Model BEFORE finding clusters

Model after finding clusters

Basically, for each cluster value in your model, you want to count all patches with the same identifier. This can be acchieved by using map. It uses a list of unique patch cluster values (remove-duplicates [cluster] of patches) and then for each entry in that list it counts all patches with this cluster value. The results are stored in a list and they represent the sizes of all your clusters. This list can be plotted as a frequency histogram by using the histogram primitive. Be sure to set the x-Axis of your plot to a plausible maximum value and set the plot pen to bar mode.

NetLogo 6 syntax:

to calc-frequency
  let freq map [[i] -> count patches with [cluster = i]] remove-duplicates [cluster] of patches

  set-current-plot "hist"
  histogram freq
end

NetLogo 5 syntax:

to calc-frequency
  let freq map [count patches with [cluster = ?]] remove-duplicates [cluster] of patches

  set-current-plot "hist"
  histogram freq
end