How to compare last 2 elements of an array?

I have an array:

array:8 [▼
  0 => array:1 [▼
    "data" => "789"
  ]
  1 => array:1 [▼
    "data" => "800"
  ]
  2 => array:1 [▼
    "data" => "789"
  ]
  3 => array:1 [▼
    "data" => "787"
  ]
  4 => array:1 [▼
    "data" => "787"
  ]
  5 => array:1 [▼
    "data" => "787"
  ]
  6 => array:1 [▼
    "data" => "787"
  ]
  7 => array:1 [▼
    "data" => "787"
  ]
]

I need to take out the last 2 elements of the array and compare them. I tried using $getLast2 = array_slice($chart_data, -2, 2, true); to get the last 2.

array:2 [▼
  6 => array:1 [▼
    "data" => "787"
  ]
  7 => array:1 [▼
    "data" => "787"
  ]
]

Which then splits it. But Im not sure how to compare these 2 elements within this new array. As the last 2 elements which are now 6 and 7 could change as more data is added. I basically need to tell if the first element is great than, less than or equal to the second element.

via Chebli Mohamed