java 如何按值类的字段对 LinkedHashMap 进行排序？
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How to sort a LinkedHashMap by its value class's field?
提问by Frank
I use the following lines to sort a LinkedHashMap, but not all items are sorted, anything wrong ?
我使用以下几行对 LinkedHashMap 进行排序，但并非所有项目都已排序，有什么问题吗？
LinkedHashMap<String,PatternData> statisticsMap;
// fill in the map ...
LinkedHashMap<String,PatternData> sortedStatisticsMap=new LinkedHashMap<String,PatternData>(); // Sort it by patternData's average
ArrayList<PatternData> statisticsMapValues=new ArrayList<PatternData>(statisticsMap.values());
Collections.sort(statisticsMapValues,Collections.reverseOrder()); // Sorting it (in reverse order)
patternData last_i=null;
for (PatternData i : statisticsMapValues) // Now, for each value
{
if (last_i==i) continue; // Without dublicates
last_i=i;
for (String s : statisticsMap.keySet()) // Get all hash keys
if (statisticsMap.get(s)==i) // Which have this value
{
sortedStatisticsMap.put(s,i);
}
}
class PatternData implements Comparable<PatternData>
{
float sum=0,average;
int totalCount=0;
Vector<String> records=new Vector<String>();
public PatternData() { }
public void add(float data)
{
sum+=data;
totalCount++;
average=sum/totalCount;
}
public void add(float data,String record)
{
add(data);
records.add(record);
}
float getAverage() { return average; }
public int compareTo(patternData o) { return (int)(average-o.average); }
}
回答by CookieOfFortune
When you return int, the range when average-o.average is between -1 and 1 will always return 0.
当你返回 int 时，average-o.average 介于 -1 和 1 之间的范围将始终返回 0。
One solution is simply change your compareTo function to:
一种解决方案是简单地将您的 compareTo 函数更改为：
return Float.compare(average, o.average);
回答by aberrant80
You're sorting floating point numbers using integers. Integers don't get rounded; they get truncated. Also, given the way you're actually doing the sorting, consider using a TreeHashMap instead.
您正在使用整数对浮点数进行排序。整数不会四舍五入；他们被截断了。此外，考虑到您实际进行排序的方式，请考虑改用 TreeHashMap。
(and just to nitpick, Java convention uses lowercase for method and variables names)
（只是为了挑剔，Java 约定对方法和变量名称使用小写字母）
