#10 Aggregating values from a collection of maps

[Anonymous]

Hi Randy,

You plugin seems to be the answer to my current project that I am building right now.

Source of my data is another server, which feeds tons of Map<string, object=""> into the aggregator framework. The value in the map is a list of java objects. My requirement is to aggregate all the value-lists. Example few records are as following - </string,>

October, Chicago, Cold, 40
January, Chicago, Freezing, -10
October, New York, Pleasant, 70
January, New York, Cold, 0
January, Toronto, Freezing, -20

Example aggregations can be,

1. (month, how-cold, count(*))
2. (month, mean-temperature)
3. (city, month, avg-temperature)

Can you tell me how will I solve this problem using jAgg.

Do note that, the values are coming in a map, and depending on which system is feeding it, the number of data-points will vary.

Thanks for your help in advance.

[Randy Gettman]

First, jAgg operates on Lists of Java objects. So you will need to extract the List out of your Map.

Then you can supply a List of properties and a List of AggregateFunctions to an Aggregation object.

Create a List of properties, assuming that your value object has getter methods such as getMonth(), getHowCold(), etc.

List<String> properties = Arrays.asList("month", "howCold");

Create your list of aggregate operations you'd like to perform.

List<AggregateFunction> aggs = new ArrayList<AggregateFunction>();
aggs.add(new CountAggregator("*"));

and/or

aggs.add(new AvgAggregator("temperature"));

Build your Aggregation object, which is what will perform the actual calculations.

Aggregation agg = new Aggregation.Builder()
   .setAggregators(aggs)
   .setProperties(properties)
   .build();

Perform the operations.

List<AggregateValue<YourType>> aggValues = agg.groupBy(yourList);

Then you can loop through the List of AggregateValue, calling getObject() to access the group-by category values and getAggregateValue(int index) to access the aggregate values.

The following documentation pages may provide further help:

• Examples
• Aggregation class
• AggregateValue class

Please reply back if you have any further questions about using jAgg.