javascript - 如果满足条件，Lodash 交换相邻的项目

Question

假设我有一个数组，[1, 2, 3, 4, 5, 3, 4, 6, 3, 7, 4]。我想交换 3 和 4 的值，前提是它们按 [3, 4] 的顺序相邻(即 [4, 3] 保持不变)。该示例的结果将是 [1, 2, 4, 3, 5, 4, 3, 6, 3, 7, 4]。

在不使用 for 循环的情况下，在 Lodash 中是否有一种优雅的方式来做到这一点？

编辑:怎么样

 _.sortBy(arr, function(value, index) {
    if (value === 3) {
        return index + 0.75;
    } else if (value === 4) {
        return index - 0.75;
    } else {
        return index
    }
});

编辑 2:进行以下操作(实际上不是 3 和 4)。

return _.reduce(tags, function(out, tag) {
    var word = tag[0];

    if (out[0] && unitPowerSuffixes.hasOwnProperty(word)) {
        out.splice(-1, 0, {
            type: 'unit-power',
            value: unitPowerSuffixes[word]
        }); // Insert one from end
    } else {
        out.push(tag);
    }

    return out;
}, []);

Answer 1

Is there an elegant way to do this in Lodash without the use of for loops?

是的，您可以按如下方式使用reduce:

var array  = [1, 2, 3, 4, 5, 3, 4, 6, 3, 7, 4];

var result = _.reduce(array, swapAdjacentInOrder(3, 4), []);

alert(JSON.stringify(result));

function swapAdjacentInOrder(a, b) {
    return function (result, element) {
        var length = result.length;

        if (length > 0 && element === b) {
            var last = length - 1;

            if (result[last] === a) {
                result[last] = b;
                element = a;
            }
        }

        result[length] = element;

        return result;
    };
}

<script src="https://rawgit.com/lodash/lodash/master/lodash.min.js"></script>

但是，swapAdjacentInOrder 函数还具有以下属性:

var array  = [3, 4, 4, 4];

var result = _.reduce(array, swapAdjacentInOrder(3, 4), []);

alert(JSON.stringify(result)); // [4, 4, 4, 3]

function swapAdjacentInOrder(a, b) {
    return function (result, element) {
        var length = result.length;

        if (length > 0 && element === b) {
            var last = length - 1;

            if (result[last] === a) {
                result[last] = b;
                element = a;
            }
        }

        result[length] = element;

        return result;
    };
}

<script src="https://rawgit.com/lodash/lodash/master/lodash.min.js"></script>

如果您不希望这样做，则可以执行以下更新的 swapAdjacentInOrder 函数:

var array  = [3, 4, 4, 4];

var result = _.reduce(array, swapAdjacentInOrder(3, 4), []);

alert(JSON.stringify(result)); // [4, 3, 4, 4]

function swapAdjacentInOrder(a, b) {
    return function (result, element) {
        var length = result.length;

        if (length > 0 && element === b) {
            var last = length - 1;

            if (result[last] !== a || last > 0 && result[last - 1] === b);
            else {
                result[last] = b;
                element = a;
            }
        }

        result[length] = element;

        return result;
    };
}

<script src="https://rawgit.com/lodash/lodash/master/lodash.min.js"></script>

希望对您有所帮助。