LINQ：双值的列表 - 后继值之间的差异 [英] Linq: List of double values - differences between successor values

问题描述

我有双重值的列表...

i have a list of double values...

1.23，1.24，1.78，1.74 ...

1.23, 1.24, 1.78, 1,74...

所以我要计算的继任者之间的区别 - >只增加（负值应先正）...上面4个值是0.01 +0,53（ - ） - $ 0.04 b $ b（ - ） - >，使其积极...

so i want to calculate the differences between the successor -> only adding (negative values should be firstly positive)... above 4 values would be 0,01 +0,53 (-)-0,04 (-) -> to make it positive...

与for循环，很容易...任何想法如何使用LINQ解决？

with an for-loop, it is easy... any idea how to solve it with linq?

推荐答案

我不知道你的意思的负面位是什么，但是这可能会做你想要什么。这是可怕的，因为它使用的副作用，但是......

I'm not sure what you mean about the negative bits, but this might do what you want. It's horrible because it uses side effects, but...

double prev = 0d;
var differences = list.Select(current =>
    {
       double diff = prev - current;
       prev = current;
       return Math.Abs(diff);
    }).Skip(1);

（第一个值被跳过，因为它只是给第一原始值和0D之间的差异。）

(The first value is skipped because it just gives the difference between the first original value and 0d.)

编辑：什么可能是略微更好将是项目的基础上对元素的扩展方法。这样可以隔离在一个地方，这是很好的副作用：

What might be slightly nicer would be an extension method to project based on pairs of elements. This isolates the side-effects in one place, which is fine:

using System.Collections.Generic;

// This must be a non-nested type, and must be static to allow the extension
// method.
public static class Extensions
{
    public static IEnumerable<TResult> SelectPairs<TSource, TResult>
        (this IEnumerable<TSource> source,
         Func<TSource, TSource, TResult> selector)
    {
        using (IEnumerator<TSource> iterator = source.GetEnumerator())
        {
           if (!iterator.MoveNext())
           {
               yield break;
           }
           TSource prev = iterator.Current;
           while (iterator.MoveNext())
           {
               TSource current = iterator.Current;
               yield return selector(prev, current);
               prev = current;
           }
        }
    }
}

要在特定情况下使用它，你会怎么做：

To use this in your particular case, you'd do:

var differences = list.SelectPairs((x, y) => Math.Abs(x-y));

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