f = -> a {
  w = a.map {|s| s.split('=')}.flatten.uniq.map.with_index.to_h
  a.each_with_object([]) {|s, acc|
    x, xa, y, ya = s.split('=').map {|k| [k, acc.find {|b| b.include? k}]}.flatten(1)
    if xa && ya then xa.concat (acc.delete ya)
    elsif xa then xa << y
    elsif ya then ya << x
    else acc << [x, y]
    end
  }.map {|a| a.sort_by {|s| w[s]}}.sort_by {|a| w[a[0]]}
}
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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