So Pinkie cloned herself using a magic mirror in the everfree forest. Her clones have no individual or distinctive character traits and are rather one-dimensional. Their only goal is to have "fun", as shown in TMPP's, and they will do whatever they can to have it.
Their mentality isn't hive-like, where the individual conforms to the group and functions as a part, even though it may appear that way. Rather, their mentality and constant desire for fun is due to the fact that they are all the exact same and were (poorly) cloned to desire only "fun". This results in them doing the exact same things, and because Pinkie Pie likes company, they hang around each other.
The Pinkie clones are very similar to the changelings:
1. no variation
2. have one goal that they will do whatever is necessary to reach (fun and get love + take over)
3. only want that one goal
4. appear to have hive-like mentality
The Changelings were all clones from the magic mirror Pinkie Pie later used to clone herself. The only exception to this is the Queen of the Changelings; she is the only different one with a distinct personality. She's not a clone.
That being said for the changelings, it is also possible that Celestia "recruited" her army with the mirror, putting non-clones higher up (like shiny armor) in the hierarchy.