EXCEL - Count unique values in range

={ SUM( 1 / COUNTIF( A1:A100, A1:A100 ) ) }

PS. For this to work, the range (e.g. A1:A100) can not contain blank cells.
PSS. This is an array function... press CTRL+ENTER once written for it to work.

MongoDB - Group stages example with match, group and sort

db.COLLECTION.aggregate([

    // 1. Filter (optional)
    {$match:
        {
            FIELD_1 : { $in: [ 'VALUE_1', 'VALUE_2' ] }
        }
    }

    // 2. Group number one
    , {$group :
        {
            _id: {
                    "FIELD_TO_GROUP_BY_1_ALIAS" : "$FIELD_TO_GROUP_BY_1"
                    , "FIELD_TO_GROUP_BY_2_ALIAS" : "$FIELD_TO_GROUP_BY_2"
            }
            , AGGREGATION_ALIAS : {$sum : "$FIELD_TO_AGGREGATE"}
        }
    }// group 1

    // 3. Match (filter on the results of the previous aggregation)
    , {$match :
        {
            population: {$gt : NUMERIC_VALUE }
        }
    }// match

    // 4. Group by
    , {$group :
        {
            _id: {"FIELD_TO_GROUP_BY_ALIAS" : "$FIELD_TO_GROUP_BY" }
            , AGGREGATION_ALIAS : { $avg : "$FIELD_TO_AGGREGATE" }
        }
    }// group 2

    // 5. Sort descending
    , {$sort :
        {
            FIELD_OR_ALIAS_TO_SORT_BY : -1
        }
    }//sort
]);

MongoDB - How to aggregate distinct children field into a single field array ($addToSet)

db.COLLECTION_NAME_HERE.aggregate([
    {$group:
        {
            _id: "$FIELD_TO_GROUP_BY_NAME_HERE"
            , AGGREGATED_FIELD_ALIAS : { $addToSet : "$FIELD_TO_AGGREGATE" }
        }
    }
]);

MongoDB - Aggregate (average) grouping by multiple fields

db.COLLECTION_NAME.aggregate([
    {$group :
        {
            _id : {
                    "FIELD_1_ALIAS" : "$FIELD_1_NAME"
                    , "FIELD_2_ALIAS" : "$FIELD_2_NAME"
            }
            , AGGREGATION_RESULT_FIELD_ALIAS : {$avg : "$FIELD_NAME"}
        }
    }
]);

MacOS - Executing/sending the contents of a file to an executable program

cat /path/filename.txt | executable_program_here


In this example, sending the contents of a .js file, to mongodb.
cat script.js | mongo

MongoDB - Basic group by with a sum

db.COLLECTION_NAME.aggregate([
    {$group:
        {
            _id : "$FIELD_TO_GROUP_BY",
            RESULTING_SUM_FIELD_ALIAS : { $sum : "$FIELD_TO_SUM"}
        }
    }
]);