A useful tidbit for those interested in playing around with Groovy. I had need recently to take a structure, or more Groovy-like, a Map, and group by a particular key, and iterate over the grouped items. Turns out to be quite easy in Groovy. Let’s see an example of such a structure and how one would normally iterate over it and display the data.

public def Example1() {
    def sampleData = [
        [ "name": "Adam Presley", "title": "Architect", "id": 1 ],
        [ "name": "Collin Judd", "title": "Dev II", "id": 15 ],
        [ "name": "Steve Goodly", "title": "Architect", id: 2 ],
        [ "name": "Chris Jordey", title: "Dev II", id: 3 ],
        [ "name": "Ben Nadel", title: "ACP", id: 5 ]
    ];

    /*
    * Display existing map.
    */
    println "Existing structure:";
    sampleData.each {
        println "Name: ${it.name}, Title: ${it.title}";
    }
    println "";
}

As you can see iteration over the structure is fairly easy. Now I want to actually group the structure items by the person’s title, iterate and display the title, then each person who has that title. Here’s how, using the same structure as above.

/*
 * Group the data by title
 */
sampleData.groupBy {
    it.title
}.each { group -> 
    println "*GROUP ${group.key}*";

    group.value.each { item ->
        println "Name: ${item.name}, Title: ${item.title}";
    }

    println "";
}

When you use the groupBy method you return, through a closure, the criteria to group by. Groovy then gives you a new structure, each key being the value to group by, which is an array of the group matches. Pretty cool!

Hope you enjoyed, and happy coding!