Flatten Arrays & flat() & flatMap()

Flatten Arrays & flat() & flatMap()

https://alligator.io/js/flat-flatmap/

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2019-08-13
 *
 * @description 编写一个程序将数组扁平化去并除其中重复部分数据，最终得到一个升序且不重复的数组
 * @augments
 * @example
 * @link https://github.com/yygmind/blog/issues/43
 *
 */

let arr = [
    [1, 2, 2],
    [3, 4, 5, 5],
    [
        6, 7, 8, 9,
        [
            11, 12,
            [
                12, 13,
                [14]
            ]
        ]
    ],
    10,
];

let log = console.log;

const autoFlatArray = (arr = []) => {
    let result = [];
    const flatArray = (arr = []) => {
        for (let i = 0; i < arr.length; i++) {
            let item = arr[i];
            if (Array.isArray(item)) {
                let temp = flatArray(item);
                result.concat(temp);
            } else {
                result.push(item);
            }
        }
    };
    flatArray(arr);
    // filter & sort asc
    result = [...new Set(result)].sort((a, b) => a > b ? 1 : -1);
    return result;
};

let result = autoFlatArray(arr);

log(`result all =`, result);
// result all = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 ]

/*
const autoFlatArray = (arr = []) => {
    let result = [];
    const flatArray = (arr = []) => {
        for (let i = 0; i < arr.length; i++) {
            let item = arr[i];
            if (Array.isArray(item)) {
                let temp = flatArray(item);
                log(`temp`, temp);
                result.concat(temp);
                log(`result 1 =`, result);
            } else {
                result.push(item);
                log(`result 2 =`, result);
            }
        }
    };
    flatArray(arr, []);
    // filter & sort asc
    result = [...new Set(result)].sort((a, b) => a > b ? 1 : -1);
    return result;
};

*/

"use strict";

/**
 *
 * @author xgqfrms
 * @license MIT
 * @copyright xgqfrms
 * @created 2019-08-13
 *
 * @description
 * @augments
 * @example
 * @link
 *
 */

let log = console.log;

var arr = [1, 2, 3, 4];

let result1 = arr.flatMap(x => [x * 2]);
// [2, 4, 6, 8]
// is equivalent to

// let result2 = arr.reduce((acc, x) => acc.concat([x * 2]), []);
// [2, 4, 6, 8]

let result2 = arr1.reduce(
    (acc, x) => {
        log(`acc =`, acc);// []
        log(`x =`, x);// 1
        let temp = acc.concat([x * 2]);
        log(`temp =`, temp);
        return temp;
    },
    [],// initialValue
);

log(`flat array flatMap`, result1);
log(`flat array reduce`, result2);

/*
arr.reduce(callback(accumulator, currentValue[, index[, array]])[, initialValue])

The reducer function takes four arguments:

Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)

*/

Array & flat

https://github.com/yygmind/blog/issues/43

https://github.com/Advanced-Frontend/Daily-Interview-Question/issues/8#issuecomment-520795766

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/flat

arr.flat(Infinity) === Infinity deep

let arr = [ [1, 2, 2], [3, 4, 5, 5], [6, 7, 8, 9, [11, 12, [12, 13, [14] ] ] ], 10];

let result = Array.from(new Set(arr.flat(Infinity))).sort((a,b)=> a > b ? 1: -1);

console.log(`flat array with unique filter & sort`, result);
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

OR

let arr = [ [1, 2, 2], [3, 4, 5, 5], [6, 7, 8, 9, [11, 12, [12, 13, [14] ] ] ], 10];

let result = [...new Set(arr.flat(Infinity))].sort((a,b)=> a > b ? 1: -1);

console.log(`flat array with unique filter & sort`, result);
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]

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