Determine the number of documents in MongoDB that meet a specific pattern using

In my database, I have records that contain various URLs, such as 

https://www.youtube.com/watch?v=blablabla
.

My goal is to tally the number of URLs for each individual site. For example: 

[{
    site: 'youtube.com',
    count: 25
},
{
    site: 'facebook.com',
    count: 135
}]

To achieve this, I attempted to use the following aggregation pipeline: 

db.getCollection('records').aggregate([
    {'$match': {'url': /.*youtube\.com.*/}}, // using youtube as an example
    {'$group': {'_id': {'site': '$url', 'count': {'$sum': 1}}}},
    {'$project': {'_id': false, 'site': '$_id.site', 'count': '$_id.count'}}
]);

The result of this pipeline is: 

[{
    "site" : "youtube.com/blablabla1",
    "count" : 1.0
},
{
    "site" : "youtube.com",
    "count" : 1.0
},
{
    "site" : "www.youtube.com/blablabla2",
    "count" : 1.0
},
{
    "site" : "www.youtube.com/blablabla1",
    "count" : 1.0
}]

However, this method is not able to accurately count identical strings.

What could be the issue with my current approach?

javascriptregexmongodbmapreduce

Answer №1

This code snippet will calculate the total number of websites:

The name of the website is identified by the following regular expression:

const testData = ['https://www.youtube.com/watch?v=UbQgXeY_zi4&list=RDUbQgXeY_zi4&index=1', 'https://www.facebook.com/maciej.kozieja.9', 'http://example.com', 'http://www.example.com']

const websites = testData.map(site => (site + '/').match(/(?:https?:\/\/)?(?:www\.)?([\w.]+)(?=\/)/)[1])

console.log(websites)

Next, we need to apply the mapReduce function to our collection:

db.collection('links').mapReduce(
    function () {
        emit((this.site + '/').match(/(?:https?:\/\/)?(?:www\.)?([\w.]+)(?=\/)/)[1], 1)
    },
    function (key, values) {
        return values.length
    }, { out: 'websiteLinksCount' }
)

After that, we can perform further operations on the data:

.then(result => {
    result.find({}).toArray((error, result) => {
        console.log(result) // This will give you an array of objects like [{_id: siteName, value: count}]
    })
})

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