Say you have \n```\n[[\'a\', \'pen\', 10],\n [\'a\', \'paper\', 20],\n [\'b\', \'paper\', 25],\n [\'a\', \'paper\', 28],\n [\'b\', \'eraser\', 29],\n [\'b\', \'eraser\', 30],\n [\'b\', \'eraser\', 39]]\n```\nreturn all consecutive combinations of size 2 by the same user\n```\n[\'pen\', \'paper\'] - 1\n[\'paper\', \'paper\'] - 1 # by a\n[\'paper\', \'eraser\'] - 1\n[\'eraser\', \'eraser\'] - 2\n```

Say you have \n\n[[\'a\', \'pen\', 10],\n [\'a\', \'paper\', 20],\n [\'b\', \'paper\', 25],\n [\'a\', \'paper\', 28],\n [\'b\', \'eraser\', 29],\n [\'b\', \'era