How to implement country-specific report in Manager

I just added new group_by filter to the latest version. So you can something like:

{% assign inventoryItemsPerUnitName = inventoryItems | group_by: "UnitName" %}

<ul>
    {% for e in inventoryItemsPerUnitName %}
    <li>{{ e.Key }}
    <ul>
        {% for inventoryItem in e.Value %}
        <li>{{ inventoryItem.Name }}</li>
        {% endfor %}
    </ul>
    {% endfor %}
</ul>

This will group inventory items by their UnitName.