ruby - Array filter using keep

i have array this:

array = ["john-56", "admin-57", "duke-58", "duke-65",           "john-56", "admin-57", "roger-65", "roger-15"]

i want keep elements duplicated, in case expect result:

["admin-57","admin-57","john-56","john-56"]

i've tried using keep_if method this:

array.keep_if { |x,y| x==y }

but leaves array empty.

maybe not more efficient, 1 line:

array.select { |x| array.count(x) == 2 }.uniq

@edit(thanks jounty)

if have values can appear more 2 times

array.select { |x| array.count(x) > 1 }.uniq

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