Javascript：使用reduce（）查找最小值和最大值？ [英] Javascript: Using reduce() to find min and max values?

问题描述

我有一个类的代码，我应该使用reduce（）方法来查找数组中的最小值和最大值。但是，我们只需要使用一次调用来减少。返回数组的大小应为2，但我知道reduce（）方法总是返回一个大小为1的数组。我可以使用下面的代码获取最小值，但是我不知道如何获取同一个电话中的最大值。我假设一旦我获得了最大值，我只需在reduce（）方法完成后将其推送到数组。

I have this code for a class where I'm supposed to use the reduce() method to find the min and max values in an array. However, we are required to use only a single call to reduce. The return array should be of size 2, but I know that the reduce() method always returns an array of size 1. I'm able to obtain the minimum value using the code below, however I don't know how to obtain the max value in that same call. I assume that once I do obtain the max value that I just push it to the array after the reduce() method finishes.

/**
 * Takes an array of numbers and returns an array of size 2,
 * where the first element is the smallest element in items,
 * and the second element is the largest element in items.
 *
 * Must do this by using a single call to reduce.
 *
 * For example, minMax([4, 1, 2, 7, 6]) returns [1, 7]
 */
function minMax(items) {
     var minMaxArray = items.reduce(
        (accumulator, currentValue) => {
             return (accumulator < currentValue ? accumulator : currentValue);
        }
    );

     return minMaxArray;
 }

推荐答案

诀窍在于提供一个empty Array as initialValue参数

The trick consist in provide an empty Array as initialValue Parameter

arr.reduce(callback, [initialValue])

initialValue [可选]用作回调
第一次调用的第一个参数的值。如果没有提供初始值，将使用数组中的第一个
元素。

initialValue [Optional] Value to use as the first argument to the first call of the callback. If no initial value is supplied, the first element in the array will be used.

所以代码看起来像这个：

So the code would look like this:

function minMax(items) {
    return items.reduce((acc, val) => {
        acc[0] = ( acc[0] === undefined || val < acc[0] ) ? val : acc[0]
        acc[1] = ( acc[1] === undefined || val > acc[1] ) ? val : acc[1]
        return acc;
    }, []);
}

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