如何将列表中的每个元素除以整数？ C＃

Question

所以我创建了一个包含双精度数的列表，是否可以用整数变量划分该列表中的每个元素？

List<Double> amount = new List<Double>();

Answer 1

Just create a new list with the modified contents:

var newAmounts = amount.Select(x => x / 10).ToList();

Creating new data is less error-prone than modifying existing data.

Answer 2

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foreach

You can iterate over each item with foreach :

foreach(var item in amount)
{
    var result = item / 3;
}

If you want to store the results in a new list you can do it inside the loop...

var newList = new List<double>(amount.Count); //<-- set capacity for performance
foreach(var item in amount)
{
    newList.Add(item / 3);
}

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LINQ

... or use Linq to an IEnumerable<double> :

var newList = from item in amount select item / 3;

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You can also use Linq extension methods:

var newList = amount.Select(item => item / 3);

Or if you want a List<double> from Linq, you can do it with ToList() :

var newList = (from item in amount select item / 3).ToList();

... or ...

var newList = amount.Select(item => item / 3).ToList();

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for

As an alternative you can use a simple for :

for (int index = 0; index < amount.Count; index++)
{
    var result = amount[index] / 3;
}

This approach will allow you to do the modifications in place:

for (int index = 0; index < amount.Count; index++)
{
    amount[index] = amount[index] / 3;
}

---

PLINQ

You may also consider using Parallel LINQ (with AsParallel ):

var newList = amount.AsParallel().Select(item => item / 3).ToList();

Warning : The result may be out of order.

This will take advantage of multicore CPU, by running the operations for each item in parallel. This is particularly good for large lists, and for operations that are independent for each item.

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Comparison

1. foreach : Easy to read and write, easy to remember. Also allows for some optimizations.
2. Linq : Better if you are used to SQL, also allows for lazy execution.
3. for : Doing the operation in place requires less memory. Allows for a more control.
4. PLinq : All you love from Linq, optimized for multiple cores. Although some caution is needed.

Answer 3

Of course the simple way is to iterate the list and divide each number:

foreach(var d in amount) {
    var result = d / 3;
}

You can store the result in a new list.

Answer 4

In case you want to modify the same instance (rather than creating a new collection), do:

for (int i = 0; i < amount.Count; ++i)
    amount[i] /= yourInt32Divisor;