C＃，max，在列表中找到面積最大的矩形

Question

我有一個矩形列表“collidedrects”我想把最大面積的那個傳遞給函數_playership.Collide（）到目前為止，我有......

var item = collidedrects.Max(x => x.Height*x.Width);
_playership.Collide(collidedrects[item]);

我不熟悉max和C＃中的=>東西

Answer 1

您可以使用Aggregate而不是Max來查找最大的矩形：

var largestRect = collidedrects.Aggregate( (r1,r2) => 
    (r1.Height * r1.Width) > (r2.Height * r2.Width) ? r1 : r2);
_playership.Collide(largestRect);

Answer 2

問題是Max返回您比較的值，而不是生成值的項。 如果您創建一個返回生成該值的項的函數MaxBy ，那么它將正常工作。

public static TSource MaxBy<TSource, TKey>(this IEnumerable<TSource> source,
    Func<TSource, TKey> selector, IComparer<TKey> comparer = null)
{
    comparer = comparer ?? Comparer<TKey>.Default;
    using (IEnumerator<TSource> sourceIterator = source.GetEnumerator())
    {
        if (!sourceIterator.MoveNext())
        {
            throw new InvalidOperationException("Sequence was empty");
        }
        TSource max = sourceIterator.Current;
        TKey maxKey = selector(max);
        while (sourceIterator.MoveNext())
        {
            TSource candidate = sourceIterator.Current;
            TKey candidateProjected = selector(candidate);
            if (comparer.Compare(candidateProjected, maxKey) > 0)
            {
                max = candidate;
                maxKey = candidateProjected;
            }
        }
        return max;
    }
}

有了這個你可以做：

var item = collidedrects.MaxBy(x => x.Height*x.Width);
_playership.Collide(collidedrects[item]);