比较2个数组，打印共有的并标记不共有的

Question

I have an example of my problem here. Take 2 arrays, 1 represents movies I have already downloaded and 1 represents movies yet to be download. I want to print a new array that is basically the 'movies yet to be downloaded' array but with flags that say "NOT DOWNLOADED" on the videos I haven't downloaded.

The twist is sometimes the videos are actually different but have the same name.

Here is the fiddle:

https://jsfiddle.net/ykhch9ng/

var websiteVidsArr = ['vid1.wmv', 'vid1.wmv', 'vid2.wmv', 'vid3.wmv', 'vid4.wmv'];
var downloadedVidsArr = ['vid1.wmv', 'vid2.wmv', 'vid3.wmv'];
var nonDownloadedVidsArr = [];

for (var i = 0; i < websiteVidsArr.length; i++) {

    if (downloadedVidsArr[i] === websiteVidsArr[i]) {
      nonDownloadedVidsArr[i] = websiteVidsArr[i];
    } else {
    nonDownloadedVidsArr[i] = websiteVidsArr[i] + ' NOT DOWNLOADED';
    }
}

console.log(nonDownloadedVidsArr);
//preferred output:
//["vid1.wmv", "vid1.wmv NOT DOWNLOADED", "vid2.wmv", "vid3.wmv", "vid4.wmv NOT DOWNLOADED"] 

Answer 1

This solution should work.

var websiteVidsArr = ['vid1.wmv', 'vid1.wmv', 'vid2.wmv', 'vid3.wmv', 'vid4.wmv'];
var downloadedVidsArr = ['vid1.wmv', 'vid2.wmv', 'vid3.wmv'];

var tempDownloadedArr = downloadedVidsArr.slice();
var nonDownloadedVidsArr = websiteVidsArr.map(function (video) {
    var downloadedIndex = tempDownloadedArr.indexOf(video);
    if (downloadedIndex === -1) {
        return video + ' NOT DOWNLOADED'
    } else {
        tempDownloadedArr.splice(downloadedIndex, 1);
        return video;
    }
})

console.log(nonDownloadedVidsArr)

Answer 2

As tadman pointed out you can do this w lodash

1. get the difference between the two _.diff , then append NOT DOWNLOADED _.map .
2. find what items downloadedVidsArr and websiteVidsArr have in common _.intersection .
3. put them together _.union

Code Below:

var websiteVidsArr = ['vid1.wmv', 'vid1.wmv', 'vid2.wmv', 'vid3.wmv', 'vid4.wmv'];
var downloadedVidsArr = ['vid1.wmv', 'vid2.wmv', 'vid3.wmv'];
var diff = _.chain(websiteVidsArr).difference(downloadedVidsArr).map(vid => `${vid}  NOT DOWNLOADED`).value();
var result = _.chain(websiteVidsArr).intersection(downloadedVidsArr).union(diff).value();