How can I spit out a list of values of a custom field, suppressing duplicate values?
For custom post named "pressmention", I want to output a file, screen echo or web page of values in its custom text field named "press_mention_information_publication-name".
However, the output should only spit out a value once.
That is to say, "pressmention" has approximately 70,000 posts. For a quantity of those (let's say, 1,000), "press_mention_information_publication-name" may have value "Wall Street Journal". But I would only want to see "Wall Street Journal" output once.
This is not for a front-end feature, it does not need to exist on WordPress. It is for my information.