根据过滤器将数组一分为二

我卖书的应用程序,当用户买了一本书,一个pdf文件被下载到手机的内存中。我有两类书,pdf文件的名称有一个代码来识别它。

   val purchasedBooks: ArrayList<String> = ArrayList()

    val directoryFiles = context?.filesDir
    val files = directoryFiles?.listFiles()


    if (files != null) {
        for (aFile in files) {
            purchasedBooks.add(aFile.name)
        }
    }

purchasedBooks :

[ssbook1.pdf, ssbook2.pdf, ssbook3.pdf, aabook1.pdf, aabook2.pdf]

val ssbooks = [ssbook1, ssbook2, ssbook3] // without .pdf
val aabooks = [aabook1, aabook2]

然后在回收视图中按部分显示:

________________
MY SS BOOK
________________
ssbook1
----------------
ssbook2
----------------
ssbook3
________________
MY AABOOK
________________
aabook1
----------------
aabook2

任何建议我都将不胜感激。