Reducer Sample Query

db.entries
    .aggregate([
        {$match: {'context.plugin': 'twitter', 'context.action': 'getTimeline', 'data.text._processed.language_tone.confidence': {$not: {$type: 10}}}},
        {$addFields: {twitter_username: { "$ifNull": [ "$data.user.screen_name._raw", "$data.screen_name._raw" ] } }},
        {$group: {_id: '$twitter_username',language_tones: {$push: '$data.text._processed.language_tone' }}},
        {$unwind: '$language_tones'},
        {$unwind: '$language_tones'},
        {$group: {_id: '$_id', scores: {$push: '$language_tones'}}},
        {$project: {_id: 1,
        //The double $$ is what's causing the issues 
            analytical: {$filter: {input: '$scores', as: 'score', cond: {$eq: ['$$score.value', 'analytical']}}},
            confidence: {$filter: {input: '$scores', as: 'score', cond: {$eq: ['$$score.value', 'confidence']}}},
            tentative: {$filter: {input: '$scores', as: 'score', cond: {$eq: ['$$score.value', 'tentative']}}},
        }},
        { "$addFields": {"analytical_average": {"$divide": [{"$reduce": {"input": "$analytical","initialValue": 0,"in": { "$add": ["$$value", "$$this.confidence"] }}},{"$cond": [{ "$ne": [ { "$size": "$analytical" }, 0 ] },{ "$size": "$analytical" }, 1]}]}},},
        { "$addFields": { "confidence_average": {"$divide": [{"$reduce": {"input": "$confidence","initialValue": 0,"in": { "$add": ["$$value", "$$this.confidence"] }}},{"$cond": [{ "$ne": [ { "$size": "$confidence" }, 0 ] },{ "$size": "$confidence" }, 1]}]}},},
        { "$addFields": {"tentative_average": {"$divide": [{"$reduce": {"input": "$tentative","initialValue": 0,"in": { "$add": ["$$value", "$$this.confidence"] }}},{"$cond": [{ "$ne": [ { "$size": "$tentative" }, 0 ] },{ "$size": "$tentative" }, 1]}]},}},
{$sort: {retweet_sum: -1, favorite_sum: -1}}

    ])