Using E4X to find distinct values in an XML list

Question

Consider this XML snippet:

 <book id="5" />
 <book id="15" />
 <book id="5" />
 <book id="25" />
 <book id="35" />
 <book id="5" />

How can I compose an E4X statement/query to get a list of the unique values in the id attribute? I'm using E4X in a JavaScript non-browser context.

5
15
25
35

Is there a distinct() or groupby() method of any kind that would help? If not, how could this be accomplished?

Answer 1

There is no unique or groupby method. However, E4X allow you to quickly create an XMLList of the values non-unique values.

var xmlSnippet = <stuff><book id="5"/>
                        <book id="15"/>
                        <book id="5"/>
                        <book id="25"/>
                        <book id="35"/>
                        <book id="5"/>
                  </stuff>;
var attributes = xmlSnippet['book'].attribute("id");

To make it unique, you can then take the XMLList, iterate through it, and store each element as the key value in an object.

var uniqueAttributes = new Object ();

for each (var a in attributes)
{
    uniqueAttributes[a] = null;
}

To access these values, iterate through them using a for in loop (not a for each in)

for (var u in uniqueAttributes)
{
// do something with u
}