This may be easier done with a hash, and that way it also doesn't matter if the "duplicates" come right after each other. Pseudo-code:

create a hash
foreach key and value pair in 2d array
  drop .\d from key
  if key exists in hash
    increase the key's value by the current value from array
  else
    add current key/value to hash

loop through hash, printing keys and values
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