Sort map values ​​in descending order with Groovy

Question

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

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

After sorting it should look like this:

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

My best attempt:

 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 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 } 

Answer 2

To do the sorting, the Tim implementation is the way to go. But if you're just wondering why your sample code doesn't work the way you expect, the answer is that the "sorted" variable should be of type LinkedHashMap, not just HashMap. You can install it explicitly:

 Map<String,Integer> sorted = new LinkedHashMap<String,Integer>() 

Or just do the following:

 Map<String,Integer> sorted = [:]