ag-grid Dropdown: Syncronize the values of two drop downs based on one of them

In the example below you can see how selecting a value in one drop down (country column) will change the options available in the second column (cities column). 

Source Code (Plunker): https://plnkr.co/edit/rmUwBcT0IvfNjHCS 

We achieve this using a function for cellEditorParams.

Note we are using a cellEditorSelector to change what type of editor we display in the 'cities' column dynamically.

• if cities map DOES have a values array defined for a country key, then we show a dropdown in the cities column

• if cities map DOES NOT have a values array defined for a country key, then we show an input field.