Set default value of select2 input

I am using select2 and I am a bit of newbie with this library. I have a page where my select2 input should set to a default value if that value is posted. Here is the html

<!-- COUNTRY -->
<span id="agency_data">
    <input type="hidden" name="country_id" id="filter_country" data-placeholder="Choose A Country Name" data-init-text="<?= isset($data['cty_name']) ? $data['cty_name'] : '' ?>" value="<?= isset($data['cty_name']) ? $data['cty_name'] : '' ?>" />
 </span> 

and this is my jQuery

        //******** COUNTRY ********
if(typeof countryId === 'undefined') {
    countryId = '';
}
if(typeof countryName === 'undefined') {
    countryName = '';
}

var dataArray = [{id:countryId,text:countryName}];

$('#filter_country').select2({
    minimumInputLength: 0,
    allowClear: true,
    ajax: {
        url: base +"/agencyList/search",
        dataType: 'json',
        type: 'POST',
        data: function (term, page) {
            return {
                country: term
            };
        },
        results: function (data, page) {
            return { 
                results: data
            };
        }
    },
    data:dataArray,
    initSelection: function (element, callback) {
        $(dataArray).each(function() {
            if (this.id == element.val()) {
                callback(this);
                return
            }
        })
    }
});

As I said I can't figure out how to set the default value of the input. I have looked at this solution but still couldn't get it to work. Any help please?

working solution

thanks to the john here is how I got it working: html:

<span id="agency_data">
                    <input type="hidden" name="ag_cty_id" id="filter_country" data-placeholder="Choose A Country Name" data-init-text="<?= isset($data['cty_name']) ? $data['cty_name'] : '' ?>" value="<?= isset($data['ag_cty_id']) ? $data['ag_cty_id'] : '' ?>" />
                </span>

jQuery:

    $('#filter_country').select2({
    minimumInputLength: 0,
    allowClear: true,
    ajax: {
        url: base +"/agencyList/search",
        dataType: 'json',
        type: 'POST',
        data: function (term, page) {
            return {
                country: term
            };
        },
        results: function (data, page) {
            return { 
                results: data
            };
        }
    },
    initSelection: function (element, callback) {

        console.log('id elemt: ' + element.val());
        callback({ id: element.val(), text: element.attr('data-init-text') });
    }
});