A follow-up to https://gist.github.com/908911 now it's showing the histogram for each slice of 3 characters.

gistfile1.rb

require 'base64'

def histogram(arr)
    arr.inject(Hash.new(0)) { |h, k| h[k] += 1; h}
end
              
def graph_histogram(h, skip_less_than)
   h.to_a.select{|v| v[1]>=skip_less_than}.sort_by{|kv| kv[1]*-1}.
     map{|a| "#{a[0]} |#{('+'*a[1])}#{a[1].to_s}\n"}.
     join
end

def caesarb64(text,n)
 base64_chars = (('A'..'Z').to_a+('a'..'z').to_a+('0'..'9').to_a+["+","/"])*2
 text.tr('A-Za-z0-9/+', base64_chars[n..n+64].join)
end

plaintext=<<EOF
The first chapter "A Scandal in Bohemia" from http://www.gutenberg.org/cache/epub/1661/pg1661.txt 
It's 19119 characters.
EOF

puts graph_histogram(histogram(Base64.decode64(caesarb64(Base64.encode64(plaintext),7)).each_char.each_slice(3)),10)
puts graph_histogram(histogram(plaintext.each_char.each_slice(3)),10)