Grails mapping sort on multiple fields :: Groovy sort on multiple map entries

grailsgroovysorting

Stumped on this one. In Grails it seems one cannot define a default sort on multiple columns in domain mapping a la static mapping = { sort 'prop1 desc, prop2 asc' }, or { sort([prop1:'desc', prop2:'asc']) }. Only first column gets sorted, lame.

Similarly, when trying to Groovy sort a Grails findAllBy query on multiple columns, the second sort overrides the first.

def list = [[rowNum:2,position:3],[rowNum:1,position:2],[rowNum:3,position:1]]

list.sort{it.rowNum}.sort{it.position}

Obviously missing the boat on the latter case, the groovy sort. I have seen postings re: implementing comparable, but looking for something more concise if possible.

Best Answer

Here is a Groovy solution. Still essentially implementing a Comparator though.

list.sort { map1, map2 -> map1.rowNum <=> map2.rowNum ?: map1.position <=> map2.position }

Related Solutions

Java – Sort a Map by values

Here's a generic-friendly version:

public class MapUtil {
    public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {
        List<Entry<K, V>> list = new ArrayList<>(map.entrySet());
        list.sort(Entry.comparingByValue());

        Map<K, V> result = new LinkedHashMap<>();
        for (Entry<K, V> entry : list) {
            result.put(entry.getKey(), entry.getValue());
        }

        return result;
    }
}

R – How to sort a dataframe by multiple column(s)

You can use the order() function directly without resorting to add-on tools -- see this simpler answer which uses a trick right from the top of the example(order) code:

R> dd[with(dd, order(-z, b)), ]
    b x y z
4 Low C 9 2
2 Med D 3 1
1  Hi A 8 1
3  Hi A 9 1

Edit some 2+ years later: It was just asked how to do this by column index. The answer is to simply pass the desired sorting column(s) to the order() function:

R> dd[order(-dd[,4], dd[,1]), ]
    b x y z
4 Low C 9 2
2 Med D 3 1
1  Hi A 8 1
3  Hi A 9 1
R>

rather than using the name of the column (and with() for easier/more direct access).

Best Answer

Related Solutions

Java – Sort a Map by values

R – How to sort a dataframe by multiple column(s)

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