Add elements to existing array

I have an array that looks like this

array(3) {
      [0]=>
      array(4) {
        ["sort"]=>
        string(0) ""
        ["day"]=>
        string(2) "2"
        ["month"]=>
        string(1) "8"
        ["year"]=>
        string(4) "2015"
      }
      [1]=>
      array(4) {
        ["sort"]=>
        string(0) ""
        ["day"]=>
        string(1) "5"
        ["month"]=>
        string(1) "8"
        ["year"]=>
        string(4) "2015"
      }
      [2]=>
      array(4) {
        ["sort"]=>
        string(0) ""
        ["day"]=>
        string(1) "9"
        ["month"]=>
        string(1) "8"
        ["year"]=>
        string(4) "2015"
      }
    }

As you can see it consists of sort, date, month and year. I want to add new element into the same array with value "day" +1.

If the 8th of august 2015 is in array the it should also include 9th of august 2015. I need a way to extract values, calculate new date and put back in all dates. The result should look like this:

array(3) {
          [0]=>
          array(4) {
            ["sort"]=>
            string(0) ""
            ["day"]=>
            string(2) "2"
            ["month"]=>
            string(1) "8"
            ["year"]=>
            string(4) "2015"
          }
          [1]=>
          array(4) {
            ["sort"]=>
            string(0) ""
            ["day"]=>
            string(1) "5"
            ["month"]=>
            string(1) "8"
            ["year"]=>
            string(4) "2015"
          }
          [2]=>
          array(4) {
            ["sort"]=>
            string(0) ""
            ["day"]=>
            string(1) "9"
            ["month"]=>
            string(1) "8"
            ["year"]=>
            string(4) "2015"
          }
          [3]=>
          array(4) {
            ["sort"]=>
            string(0) ""
            ["day"]=>
            string(2) "3"
            ["month"]=>
            string(1) "8"
            ["year"]=>
            string(4) "2015"
          }
          [4]=>
          array(4) {
            ["sort"]=>
            string(0) ""
            ["day"]=>
            string(1) "6"
            ["month"]=>
            string(1) "8"
            ["year"]=>
            string(4) "2015"
          }
          [5]=>
          array(4) {
            ["sort"]=>
            string(0) ""
            ["day"]=>
            string(1) "10"
            ["month"]=>
            string(1) "8"
            ["year"]=>
            string(4) "2015"
          }
        }

Ideally it should also exclude new dates, if allready identical date is in the array.

via Chebli Mohamed