检查列表中的任何项目是否与另一个列表中的任何项目匹配 [英] Check if any item in a list matches any item in another list

问题描述

一个同事要我写一个单行代码来替换以下方法：

A coleague asked me to write a one-liner to replace the following method:

public static bool IsResourceAvailableToUser(IEnumerable<string> resourceRoles, IEnumerable<string> userRoles)
{
    foreach (var userRole in userRoles)
        foreach (var resourceRole in resourceRoles)
            if (resourceRole == userRole)
                return true;
    return false;
}

Resharper，我想到了：

Resharper and I came up with this:

public static bool IsResourceAvailableToUser(IEnumerable<string> resourceRoles, IEnumerable<string> userRoles)
{
    return userRoles.Where(resourceRoles.Contains).Count() > 0;
}

还有更好的方法吗？

推荐答案

您可以编写可处理许多情况的通用扩展方法。该功能本身的实质是一行。

You could write a generic extension method that would handle many cases. The meat of the function itself is one line.

/// <summary>
/// Compares both lists to see if any item in the enumerable 
/// equals any item in the other enumerable. 
/// </summary>
public static bool AnyItem<T>(this IEnumerable<T> source, IEnumerable<T> other, IEqualityComparer<T> comparer = null)
{
    return (comparer == null ? source.Intersect(other) : source.Intersect(other, comparer)).Any();
}

较旧，效率较低的答案

Older, Less efficient answer

public static bool AnyItem<T>(this IEnumerable<T> source, IEnumerable<T> other)
{
    return source.Any(s => other.Any(o => EqualityComparer<T>.Default.Equals(s, o)));
}

我认为比当前答案更有效（不是）。我将不得不检查获取EqualityComparer是否昂贵，但我对此表示怀疑。

I think this is also more efficient than the current answer (It's not). I would have to check if getting the EqualityComparer is expensive, but I'm willing to doubt it.

您还可以扩展此函数以接受一个表达式，该表达式将评估与包含对象的可枚举进行比较的属性。

You could also extend this function to accept an Expression that would evaluate what properties to compare for enumerables that contain objects.

public static bool AnyItem<T, TResult>(
        this IEnumerable<T> source, 
        IEnumerable<T> other, 
        Expression<Func<T, TResult>> compareProperty = null)
{
    if (compareProperty == null)
    {
        return source.Any(s => other.Any(o => EqualityComparer<T>.Default.Equals(s, o)));
    }

    return source.Any(s => other.Any(o => 
                    EqualityComparer<TResult>.Default.Equals(
                    s.GetPropertyValue(compareProperty),
                    o.GetPropertyValue(compareProperty))));
}

public static TValue GetPropertyValue<TTarget, TValue>(
    this TTarget target, Expression<Func<TTarget, TValue>> memberLamda)
{
    var memberSelectorExpression = memberLamda.Body as MemberExpression;
    var property = memberSelectorExpression?.Member as PropertyInfo;
    return (TValue)property?.GetValue(target);
}

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