如果元素的计数小于“n”，则删除数组中的所有相似元素

Question

我有一个包含数千个元素的数组，其中许多元素是其他元素的副本。我需要的是一种方法来查找数组中'foo'元素的计数，如果小于'n'，则从数组中删除'foo'的所有元素。

我需要的示例

string[] words = new string[]
int n = 8;
int k = Occurances of "foo" in words;
if (k < n) {
    //Remove all occurances of 'foo' in the array
}

如果数组 'words' 中的起始元素是

{"foo","foo","foo","foo","foo","foo","foo","bar","bar","bar","bar","bar","bar","bar","bar","bar"}

结果将是数组中的左下角，因为只找到了 7 次出现的“foo”，但发现了 9 次出现的“bar”

{"bar","bar","bar","bar","bar","bar","bar","bar","bar"}

感谢任何帮助

Answer 1

您可以使用 LINQ GroupBy 和 Count 来实现：

string[] words = new string[] { "foo", "foo", "foo", "foo", "foo", "foo", "foo", "bar", "bar", "bar", "bar", "bar", "bar", "bar", "bar", "bar" };
int n = 8;
var groups = words.GroupBy(x => x).Where(g => g.Count() >= n);

您在这里所做的是按元素值（foo 组和 bar 组）对元素进行分组，并对每个组进行计数，得到元素数量大于某个阈值的组（在您的情况下为 n = 8）

要取回数组，您只需使用SelectMany 进一步改进：

string[] filteredWords = words.GroupBy(x => x).Where(g => g.Count() >= n)
    .SelectMany(g => g).ToArray();

Answer 2

这很有效，它保留了元素的原始顺序。

var words = new[]
{
    "foo", "foo", "foo", "foo", "foo",
    "foo", "foo", "bar", "bar", "bar",
    "bar", "bar", "bar", "bar", "bar",
    "bar"
};

var keepers = new HashSet<string>(
    words.ToLookup(x => x).Where(x => x.Skip(7).Any()).Select(x => x.Key));

words = words.Where(w => keepers.Contains(w)).ToArray();

如果顺序不重要，那么就可以了：

words =
    words
        .ToLookup(x => x)
        .Where(x => x.Skip(7).Any())
        .SelectMany(x => x)
        .ToArray();

---

根据您的评论，“是否可以进一步扩展它，并检查字符串的某些部分是否出现？”，我假设您的意思是您要计算“单词”部分的单个频率如果满足频率要求，则保留整个“单词”。这可能不是很清楚。这是我的代码：

var words = new[]
{
    "foo", "foo", "foo extrabits", "foo", "foo",
    "foo", "foo", "bar", "bar", "bar",
    "bar", "bar", "bar extrabits", "bar", "bar",
    "bar"
};

var keepers =
    new HashSet<string>(
        words
            .SelectMany(x => x.Split(' '))
            .ToLookup(x => x)
            .Where(x => x.Skip(7).Any())
            .Select(x => x.Key));

words =
    words
        .Where(x => x.Split(' ').Any(y => keepers.Contains(y)))
        .ToArray();

这会产生：

酒吧 酒吧 酒吧 酒吧 酒吧 酒吧外卖 酒吧 酒吧 酒吧