Filter out maps from a list of maps based on values inside the map in Java groovy

Question

I have a list of maps, with 3 key/values like this:

[
  [name: name1, date: Sat Oct 01 00: 00: 00 CEST 2021, doc: doc1],
  [name: name2, date: Sun Oct 14 00: 00: 00 CEST 2021, doc: doc1],
  [name: name2, date: Sat Oct 23 00: 00: 00 CEST 2021, doc: doc2],
//[name: name2, date: Sat Oct 15 00: 00: 00 CEST 2021, doc: doc2],
  [name: name2, date: Sat Oct 04 00: 00: 00 CEST 2021, doc: doc3],
  [name: name2, date: Sat Oct 11 00: 00: 00 CEST 2021, doc: doc4],
  [name: name3, date: Sat Oct 20 00: 00: 00 CEST 2021, doc: doc1],
  [name: name3, date: Sat Oct 03 00: 00: 00 CEST 2021, doc: doc2],
]

I need to find the most recent date for any given combination of name and doc, so for example if i have two docs of the same type for any given name i need to filter out all but the one with the most recent date.

In this case, I need to filter out the commented out line as another map with the same kind of name and doc exist with more recent date.

How can I accomplish this using a list of maps in Java Groovy?

Answer 1

You can groupBy your list over the values of the keys you want to group (eg name and doc ). Then collectMany over the resulting map: if there is only one item in the value , return it; otherwise reverse sort the items by the values of your sort-key (eg date ) and return the tail .