BigDecimal 汇总统计 [英] BigDecimal summary statistics
本文介绍了BigDecimal 汇总统计的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我有一个 BigDecimals 列表.
I have a list of BigDecimals.
List<BigDecimal> amounts = new ArrayList<>()
如何使用 Java 8 流获取上述列表的汇总统计数据,而不会丢失 BigDecimal 的最多 3-4 个小数位的精度?
How do i get the summary statistics of the above list using Java 8 streams without losing precision of upto 3-4 decimal places of the BigDecimal?
推荐答案
我创建了 这个答案,允许扩展它以支持求和,因此也计算平均值:
I created a BigDecimal
specialization of the generic summary statistics collector of this answer, which allowed extending it to also support summing, hence also calculating an average:
/**
* Like {@code DoubleSummaryStatistics}, {@code IntSummaryStatistics}, and
* {@code LongSummaryStatistics}, but for {@link BigDecimal}.
*/
public class BigDecimalSummaryStatistics implements Consumer<BigDecimal> {
public static Collector<BigDecimal,?,BigDecimalSummaryStatistics> statistics() {
return Collector.of(BigDecimalSummaryStatistics::new,
BigDecimalSummaryStatistics::accept, BigDecimalSummaryStatistics::merge);
}
private BigDecimal sum = BigDecimal.ZERO, min, max;
private long count;
public void accept(BigDecimal t) {
if(count == 0) {
Objects.requireNonNull(t);
count = 1;
sum = t;
min = t;
max = t;
}
else {
sum = sum.add(t);
if(min.compareTo(t) > 0) min = t;
if(max.compareTo(t) < 0) max = t;
count++;
}
}
public BigDecimalSummaryStatistics merge(BigDecimalSummaryStatistics s) {
if(s.count > 0) {
if(count == 0) {
count = s.count;
sum = s.sum;
min = s.min;
max = s.max;
}
else {
sum = sum.add(s.sum);
if(min.compareTo(s.min) > 0) min = s.min;
if(max.compareTo(s.max) < 0) max = s.max;
count += s.count;
}
}
return this;
}
public long getCount() {
return count;
}
public BigDecimal getSum()
{
return sum;
}
public BigDecimal getAverage(MathContext mc)
{
return count < 2? sum: sum.divide(BigDecimal.valueOf(count), mc);
}
public BigDecimal getMin() {
return min;
}
public BigDecimal getMax() {
return max;
}
@Override
public String toString() {
return count == 0? "empty": (count+" elements between "+min+" and "+max+", sum="+sum);
}
}
它可以类似于 DoubleSummaryStatistics
对应物使用,比如
It can be used similar to the DoubleSummaryStatistics
counterpart, like
BigDecimalSummaryStatistics bds = list.stream().collect(BigDecimalSummaryStatistics.statistics());
作为一个完整的例子:
List<BigDecimal> list = Arrays.asList(BigDecimal.ZERO, BigDecimal.valueOf(-2), BigDecimal.ONE);
BigDecimalSummaryStatistics bds = list.stream().collect(BigDecimalSummaryStatistics.statistics());
System.out.println(bds);
System.out.println("average: "+bds.getAverage(MathContext.DECIMAL128));
3 elements between -2 and 1, sum=-1
average: -0.3333333333333333333333333333333333
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