select a distinct string value out of series of string iteration.

[Virangya]

hi,

how can i select only unique string out of a series of iterating strings?
for example, i have this folder which contains number of files with quite long names.
i have used readdir() to find all the files.
assume that the name of the file has an format.
eg: "some_name_string(a_string)(a_date).html"
now when i iterate these names i want to display pages which has (a_string) value a unique one. like using DISTINCT in database,(distinct (a_string) value)
how can i d this.. i have no idea. Please help me out,
thanks in advance.

[Virangya]

ok i found it myself , unique_array();