MapReduce function

my_code_example_4.md

Calculate most used hashtags (JavaScript)

AWS Lambda function to calculate most used hashtags from an Instagram account. The Instagram posts are stored in a DynamoDB table.

var doc = require('dynamodb-doc');
var dynamo = new doc.DynamoDB();
var mapreduce = require('mapred')(1);

// POST /igCalcPopularTags
// params:
// +ig_user_id:   instagram user id
// +user_id:      app devise user id
exports.igCalcPopularTags = function(event, context) {
  if(event.ig_user_id !== null) {
    var ig_user_id = parseInt(event.ig_user_id);

    // DynamoDB params
    var dynParamsQ1 = {};
    dynParamsQ1.TableName = "IGMedia";
    dynParamsQ1.IndexName = "IndexUserYear";
    dynParamsQ1.KeyConditions = [dynamo.Condition("ig_user_id", "EQ", ig_user_id)];

    dynamo.query(dynParamsQ1, function(err, data) {
      if(err) {
        console.log(err, err.stack);
        context.fail('DynamoDB query failed');
      }
      else {
        var tagsData = [];
        for (var i = 0, len = data.Count; i < len; i++) {
          if(data.Items[i].tags != undefined) {
            tagsData.push([data.Items[i].media_id, data.Items[i].tags]);
          }
        }

        mapreduce(tagsData,
          // map
          function(key, value) {
            var list = [], aux = {};
            value = value.split(',');
            value.forEach(function(w){
              aux[w] = (aux[w] || 0) + 1;
            });
            for(var k in aux){
              list.push([k, aux[k]]);
            }
            return list;
          },
          // reduce
          function(key, values) {
            var sum = 0;
            values.forEach(function(e){
              sum += e;
            });
            return sum;
          },
          function(MRresult) {
            // Sort results DESC
            var tagsSortable = Object.keys(MRresult).sort(function(a, b) { return -(MRresult[a] - MRresult[b]) });
            // Select only top 5
            tagsSortable = tagsSortable.slice(0,5);

            // DynamoDB params
            var dynParams = {};
            dynParams.TableName = "IGStatsGlobal";
            dynParams.Key = {'ig_user_id': ig_user_id};
            dynParams.UpdateExpression = "set popular_tags = :tags";
            dynParams.ExpressionAttributeValues = {":tags" : tagsSortable};

            // Save to DynamoDB
            dynamo.updateItem(dynParams, function(err, data) {
              if(err) {
                console.log(err, err.stack);
              } else {
                context.succeed({
                  result:        "ok",
                  user_id:       event.user_id,
                  popular_tags:  tagsSortable
                });
              }
            });
          }
        );
      }
    });
  }
  else {
    context.fail('No ig_user_id provided');
  }
};