JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.4/themes/ui-lightness/jquery-ui.css">
<div rel="one"></div>
<div rel="one"></div>
<div rel="two"></div>
<div rel="one"></div>
<div rel="three"></div>
<div rel="three"></div>
<div rel="one"></div>

JavaScript

$.map = function( elems, callback, arg ) {
    var value, key, ret = [],
        i = 0,
        length = elems.length,
        // jquery objects are treated as arrays
        isArray = elems instanceof jQuery || length !== undefined && typeof length === "number" && ( ( length > 0 && elems[ 0 ] && elems[ length -1 ] ) || length === 0 || jQuery.isArray( elems ) ) ;

    // Go through the array, translating each of the items to their
    if ( isArray ) {
        for ( ; i < length; i++ ) {
            value = callback( elems[ i ], i, ret, arg );

            if ( value != null ) {
                ret[ ret.length ] = value;
            }
        }

    // Go through every key on the object,
    } else {
        for ( key in elems ) {
            value = callback( elems[ key ], key, ret, arg );

            if ( value != null ) {
                ret[ ret.length ] = value;
            }
        }
    }

    // Flatten any nested arrays
    return ret.concat.apply( [], ret );
};


var arr = 
$.map($('div'), function( v, i, arr ) { 
    var rel = $(v).attr('rel'); 
    return $.inArray( rel, arr ) === -1 ? rel : void 0;
});

document.write( arr );