PHP offers a host of built in functions that we can use for sorting arrays. These functions allow us to sort arrays by key/value or ascending/decending order.

• a: an prefix a, to function means the function sorts by value but maintains the association between key/value pairs the way it was.
• k: an prefix k, to function means the function sorts by key but maintains the key/value associations.
• The lack of k or a means the the function sorts by value but does not maintain the key/value association.
• r: The prefix r, to function means the sorting order will be reversed.

• u: The prefix u, to function means that a second argument is expected, the name of the user-defined function that specifies the ordering of any two elements that are being sorted.

                                       
  
  Array Sorting Functions
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  Function                                                  Behavior
  asort()                                                     Takes a single array as argument