Getting grouped (distinct?!?) array of values from Cosmos SQL - azure-cosmosdb

Question

Given a collection of Cosmos documents similar to the following, I'd like to generate a grouped (distinct?!?) list of "categories" using Cosmos SQL. Any help in this regard would be greatly appreciated.
[
{
"id": "f0136e76-8e66-6a5a-3790-b577001d6420",
"itemId": "analyze-and-visualize-your-data-with-azure-cosmos-db-notebooks",
"title": "Built-in Jupyter notebooks in Azure Cosmos DB are now available",
"categories": [
"Developer",
"Database",
"Data Science"
]
},
{
"id": "f0136e76-8e66-6a5a-3790-b577001d6420",
"itemId": "analyze-and-visualize-your-data-with-azure-cosmos-db-notebooks",
"title": "Built-in Jupyter notebooks in Azure Cosmos DB are now available",
"categories": [
"Developer",
"Database",
"Data Science"
]
},
{
"id": "d98c1dd4-008f-04b2-e980-0998ecf8427e",
"itemId": "improving-azure-virtual-machines-resiliency-with-project-tardigrade",
"title": "Improving Azure Virtual Machines resiliency with Project Tardigrade",
"categories": [
"Virtual Machines",
"Supportability",
"Monitoring"
]
}
]

Answer 1

GroupBY is not supported by Azure CosmosDB so far. You can alternatively use Stored Procedure to implement your requirement.
Base on the sample documents you have given above, here is a sample stored Procedure
function groupBy() {
var collection = getContext().getCollection();
var collectionLink = collection.getSelfLink();
var isValid = collection.queryDocuments(
collectionLink,
'SELECT * FROM stackoverflow s',
{EnableCrossPartitionQuery: true},
function (err, feed, options) {
if (err) throw err;
if (!feed || !feed.length) {
var response = getContext().getResponse();
console.log(JSON.stringify(response));
response.setBody('no docs found');
}
else {
var response = getContext().getResponse();
var items = {};
for(var i=0;i<feed.length;i++){
var categories = feed[i].categories;
for(var j=0;j<categories.length;j++){
items[categories[j]] = categories[j]
}
var distinctArray = [];
for(var distinctObj in items){
distinctArray.push(items[distinctObj]);
}
}
response.setBody(distinctArray);
}
});
if (!isValid) throw new Error('Kindly check your query, which not accepted by the server.');
}