mongodb count num of distinct values per field key

Question

Is there a query for calculating how many distinct values a field contains in DB   f e I have a field for country and there are 8 types of country values  spain  england  france  etc      If someone adds more documents with a new country I would like the query to return 9   Is there easier way then group and count

User · Answer

With MongoDb 3 4 4 and newer  you can leverage the use of  arrayToObject operator and a  replaceRoot pipeline to get the counts    For example  suppose you have a collection of users with different roles and you would like to calculate the distinct counts of the roles  You would need to run the following aggregate pipeline   db users aggregate           group               id       toLower     role              count       sum   1                    group               id   null           counts                   push      k      id    v     count                               replaceRoot              newRoot       arrayToObject     counts                     Example Output         user    67       superuser    5       admin    4       moderator    12

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Here is example of using aggregation API  To complicate the case we re grouping by case-insensitive words from array property of the document   db articles aggregate                  match                keywords     not    size  0                            unwind    keywords                    group                 id    toLower    keywords                count     sum  1                                   match                count     gte  2                           sort     count   -1            limit   100         that give result such as      id     inflammation    count    765       id     obesity    count    641       id     epidemiology    count    617       id     cancer    count    604       id     breast cancer    count    596       id     apoptosis    count    570       id     children    count    487       id     depression    count    474       id     hiv    count    468       id     prognosis    count    428

User · Answer

I use this query  var collection    quot countries quot   var field    quot country quot    db collection  distinct field  forEach function value  print field    quot    quot    value    quot    quot    db hosts count   field   value       Output  countries  England  3536 countries  France  238 countries  Australia  1044 countries  Spain  16  This query first distinct all the values  and then count for each one of them the number of occurrences

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You can leverage on Mongo Shell Extensions  It s a single  js import that you can append to your  HOME  mongorc js  or programmatically  if you re coding in Node js io js too   Sample  For each distinct value of field counts the occurrences in documents optionally filtered by query       db users distinctAndCount  name    name    a i          Abagail   1     Abbey   3     Abbie   1            The field parameter could be an array of fields       db users distinctAndCount   name   job     name    a i          Austin Educator    1     Aurelia Educator    1     Augustine Carpenter    1

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I wanted a more concise answer and I came up with the following using the documentation at aggregates and group db countries aggregate    quot  group quot     quot  id quot    quot  country quot    quot count quot    quot  sum quot   1

User · Answer

To find distinct in field 1 in collection but we want some WHERE condition too than we can do like following    db your collection name distinct  field 1    WHERE condition here and it should return a document    So  find number distinct names from a collection where age   25 will be like    db your collection name distinct  names     age      gt   25     Hope it helps

User · Answer

MongoDB has a distinct command which returns an array of distinct values for a field  you can check the length of the array for a count   There is a shell db collection distinct   helper as well    gt  db countries distinct  country       Spain    England    France    Australia      gt  db countries distinct  country   length 4

[mongodb] mongodb count num of distinct values per field/key

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