Sorting Map values in descending order with Groovy

Question

I have a Map<String,Integer> whose entries (keys) need to be sorted in order of descending value. For instance, if the map looks like:

"a" => 5
"b" => 3
"c" => 12
"d" => 9

The after sorting it needs to look like:

"c" => 12
"d" => 9
"a" => 5
"b" => 3

My best attempt thus far:

def test() {
    Map<String,Integer> toSort = new HashMap<String,Integer>()
    toSort.put("a", 5)
    toSort.put("b", 3)
    toSort.put("c", 12)
    toSort.put("d", 9)

    Map<String,Integer> sorted = sortMapDesc(toSort)
    sorted.each {
        println "${it.key} has a value of ${it.value}."
    }
}

def sortMapDesc(Map<String,Integer> toSort) {
    println "Sorting..."
    println toSort

    // The map of properly sorted entries.
    Map<String,Integer> sorted = new HashMap<String,Integer>()

    // Keep scanning the map for the key with the highest value. When we find
    // it, add it as the next entry to the 'sorted' map, and then zero it out
    // so it won't show up as the highest on subsequent scans/passes. Stop scanning
    // when the entire 'toSort' map contains keys with zeros.
    while(!mapIsAllZeros(toSort)) {
        int highest = -1
        String highestKey = ""
        toSort.each {
            if(it.value > highest) {
                highest = it.value
                highestKey = it.key
            }
        }

        toSort.put(highestKey, 0)
        sorted.put(highestKey, highest)
    }

    sorted
}

def mapIsAllZeros(Map<String,Integer> toCheck) {
    toCheck.values().every{!it}
}

When I run test() I get the following output:

Sorting...
[d:9, b:3, c:12, a:5]
d has a value of 9.
b has a value of 3.
c has a value of 12.
a has a value of 5.

Where am I going wrong here?

Answer 1

Just do:

​def m = [a:​5, b:12, c:3, d:9]
def sorted = m.sort { a, b -> b.value <=> a.value }