按频率对 Javascript 数组进行排序，然后过滤重复项

获取 javascript 数组，按值的频率排序，然后过滤唯一值的优雅方法是什么？

So,

["apples", "oranges", "oranges", "oranges", "bananas", "bananas", "oranges"]

becomes

["oranges, "bananas", "apples"]

首先计算每个项目的频率。

{
    apples: 1,
    oranges: 4,
    bananas: 2
}

然后从此频率对象创建一个数组，该数组也将删除重复项。

["apples", "oranges", "bananas"]

现在使用我们之前创建的频率图按降序排列该数组。

function compareFrequency(a, b) {
    return frequency[b] - frequency[a];
}

array.sort(compareFrequency);

这是完整的源代码（使用新引入的数组函数 https://developer.mozilla.org/en/new_in_javascript_1.6#Array_extras在 ECMA 5 中）并结合重复数据删除和频率图生成步骤，

function sortByFrequency(array) {
    var frequency = {};

    array.forEach(function(value) { frequency[value] = 0; });

    var uniques = array.filter(function(value) {
        return ++frequency[value] == 1;
    });

    return uniques.sort(function(a, b) {
        return frequency[b] - frequency[a];
    });
}

与上面使用常规数组迭代相同。

function sortByFrequencyAndRemoveDuplicates(array) {
    var frequency = {}, value;

    // compute frequencies of each value
    for(var i = 0; i < array.length; i++) {
        value = array[i];
        if(value in frequency) {
            frequency[value]++;
        }
        else {
            frequency[value] = 1;
        }
    }

    // make array from the frequency object to de-duplicate
    var uniques = [];
    for(value in frequency) {
        uniques.push(value);
    }

    // sort the uniques array in descending order by frequency
    function compareFrequency(a, b) {
        return frequency[b] - frequency[a];
    }

    return uniques.sort(compareFrequency);
}