vb.net ArrayList 中值的总和
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Total sum of values in an ArrayList
提问by friend
Dim arrLst As New ArrayList
Dim dblVal as Double
this arrLstconstists of n number of values(Double)
这arrLst由 n 个值组成 ( Double)
at present i use the following piece of code to calculate the sum of
values in arrLst
目前我使用以下代码来计算值的总和 arrLst
For i = 0 To arrLst .Count - 1
If dblVal = 0.0 Then
dblVal = arrLst .Item(i)
Else
dblVal = dblVal + arrLst.Item(i)
End If
Next
as arrList.Sum()is not available in VB.NET, is there any other method to do the same job ?
由于arrList.Sum()在 中不可用VB.NET，是否还有其他方法可以完成相同的工作？
回答by Guffa
Well, first of all, an ArrayListis not a good choice to store values of the same type. You should rather use a List(Of Double), then each value doesn't have to be cast to double when you access it.
嗯，首先， anArrayList不是存储相同类型值的好选择。您应该使用 a List(Of Double)，然后在访问每个值时不必将其强制转换为 double 。
Anyhow, you can make your code a lot simpler by just setting the sum to zero before you start:
无论如何，您可以在开始之前将总和设置为零，从而使您的代码更简单：
dblVal = 0.0
For i = 0 To arrLst.Count - 1
dblVal = dblVal + arrLst.Item(i)
Next
(I know that the variable is zero by default when you declare it, so you could actually skip setting it to zero, but it's good to actually set values that the code relies on.)
（我知道在声明变量时默认情况下该变量为零，因此您实际上可以跳过将其设置为零，但实际设置代码所依赖的值是很好的。）
Using For eachand the +=operator it gets even simpler:
使用For each和+=操作符变得更加简单：
dblVal = 0.0
For Each n In arrLst
dblVal += n
Next
You can also use the method Sumto add all the values, but as you use an ArrayListyou have to make it a collection of doubles first:
您还可以使用该方法Sum添加所有值，但是当您使用 an 时，ArrayList您必须先使其成为双精度集合：
dblVal = arrLst.Cast(of Double).Sum()
回答by Zohar Peled
Try this:
尝试这个：
dblVal = 0
arrLst.OfType(Of Double)().ToList(Of Double)().ForEach(Function(dbl) dblVal += dbl)
回答by Nilesh Patel
Try this.
尝试这个。
double doubleSum = doubleList.stream().mapToDouble(Double::doubleValue).sum();
