require 'set'
f = -> a {
  h = a.map {|s| s.split('=')}.flatten.uniq.map.with_index.to_h
  a.each_with_object([]) {|s, acc|
    x, xs, y, ys = s.split('=').map {|k| [h[k], acc.find {|b| b.include? h[k]}]}.flatten(1)
    if xs && ys then xs.merge(acc.delete ys)
    elsif xs then xs << y
    elsif ys then ys << x
    else acc << SortedSet[x, y]
    end
  }.sort_by(&:first).map {|a| a.map &h.invert.method(:[]) }
}
a = ["a1=a2", "b1=b2", "b3=b2", "c1=c2", "e1=e2",
"a3=a4", "c3=c4", "e1=e3", "a2=a4", "c3=c1",
"b3=a4", "c2=d1", "a4=a5", "d2=c1", "b4=b3", "d3=c3"]
p f.(a)
 

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