Most efficient way to create searchable "array" in VB.NET

I would like to create a multidimensional array of some description in VB.NET that can store and search the following data efficiently (search on the second dimension, to return the first).

>Solution :

Dim data As New Dictionary(Of String, String) From {
    {"xls",  "excel"},
    {"xlsx", "excel"},
    {"doc",  "word"},
    {"docx", "word"},
    {"ppt",  "powerpoint"},
    {"pptx", "powerpoint"}
}

Access it like this:

Dim ext As String = "docx"
Dim folder As String = data(ext)