Sort List<Map<String,Object>> based on value

Question

Basically I have a List<Map<String,Object>>, and I want to sort it by the values of certain key in the map.

The problem is that I do not know the type... This map can contain Strings, Integers, Doubles, Floats etc.... I would like to sort it:

So far

List<Map<String,Object>> data = getResults();
Collections.sort(data, (o1, o2) -> (String.valueOf(o2.get("Field1")))
              .compareTo((String.valueOf(o1.get("Field1")))));

It is not a great Idea since numbers are not properly sorted.... How can I handle this?

Answer 1

You can generalize comparing numbers by comparing their double values, because they are the largest. If two objects cannot be cast to numbers and the double value cannot be parsed from these objects, then compare their string values:

List<Map<String, Object>> data = Arrays.asList(
        Map.of("Field1", 21.2d),  // Double
        Map.of("Field1", "qqq"),  // String
        Map.of("Field1", "22.5"), // String
        Map.of("Field1", 2),      // Integer
        Map.of("Field1", 3L),     // Long
        Map.of("Field1", 23.1f)); // Float

data.sort(Comparator.comparingDouble((Map<String, Object> map) -> {
    Object object = map.get("Field1");
    if (object instanceof Number) {
        return ((Number) object).doubleValue();
    } else {
        try {
            return Double.parseDouble(String.valueOf(object));
        } catch (NumberFormatException e) {
            return Double.NaN;
        }
    }
}).thenComparing(map -> String.valueOf(map.get("Field1"))));

data.forEach(System.out::println);
// {Field1=2}
// {Field1=3}
// {Field1=21.2}
// {Field1=22.5}
// {Field1=23.1}
// {Field1=qqq}

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^{See also: Sort 2D List by Column Header}