How do I order an array by neither ASC or DESC ?

[Antivirus]

I have an array of values such as follows: '4,8,8,7,4,7,8'

and I want to them order them in the following order: 7,4,8

so that the array orders like this: '7,7,4,4,8,8,8'

Is there a function (in php or mysql) which defines custom sort orders? I have been searching the php manual but can't seem to find anything