Steps:
1. Create a State Definition with 26 Characters as option. Keep Style same so that they look same.
2. In the Mashup; Add a Radio Button list and select ButtonStates as State Definition created in Step 1.
3. Create a Service which takes a character as Input and filter the Data. You can use Query to filter the data
example:
var params = {
maxItems: undefined /* NUMBER */
};
// result: INFOTABLE
var result1 = Things["TestDataTable1"].GetDataTableEntries(params);
var params = {
inclusive: true /* BOOLEAN */,
fieldName: "source" /* STRING */,
t: result1 /* INFOTABLE */,
pattern: "A*" /* STRING */
};
// result: INFOTABLE
var result = Resources["InfoTableFunctions"].LikeFilter(params);
4. Bind the SelectedText of the Radio Button to the service input parameter.
5. Bind the SelectionChanged to the service to call the service when the selection changes.
I hope it helps.