Sorting an array

I have a 2-d array: $list[$ctr]["username"] $list[$ctr]["county"] $list[$ctr]["age"] $list[$ctr]["id"] $list[$ctr]["days"] I need to sort by days, which is an integer. What function should I use? E.g., $list[0][mark] $list[0][somewhere] $list[0][12] $list[0][1] $list[0][200] $list[1][andy] $list[1][somewherefurther] $list[1][18] $list[1][2] $list[1][100] $list[2][sam] $list[2][somewhereelse] $list[2][15] $list[2][3] $list[2][150] should sort to: $list[0][mark] $list[0][somewhere] $list[0][12] $list[0][1] $list[0][100] $list[1][andy] $list[1][somewherefurther] $list[1][18] $list[1][2] $list[1][150] $list[2][sam] $list[2][somewhereelse] $list[2][15] $list[2][3] $list[2][150] -- Random (non-anti-Microsoft) fortune