Build complex queries with multiple fields in cloudant - cloudant

Question

Date State | City | Zip | Water | Weight
-------------------------------------------------------------------
01/01/2016 Arizona Chandler 1011 10 ltr 40 kg
01/04/2016 Arizona Mesa 1012 20 ltr 50 kg
06/05/2015 Washington Spokane 1013 30 ltrs 44 kg
06/08/2015 Washington Spokane 1013 30 ltrs 44 kg
What I want are complex queries, like I want to know average water, weight by passing a city or state or ip for a date range or month, or any field or all fields.
I am not sure how to go about this. Read about map reduce, but cant guess how will I get above output
If you have link for examples which covers above scenarios that will also help.
Thanks in advance

Answer 1

So first we need to model your structured data in JSON. Something like this would work:
{
"date": "2016-01-01",
"location": "Arizona Chandler",
"pressure": 1101,
"water": 10,
"weight": 40
}
Here's your data in a Cloudant database:
https://reader.cloudant.com/so37613808/_all_docs?include_docs=true
Next we'd need to create a MapReduce view to aggregate the a specific field by date. A map function to create an index whose key is the date and whose value is the water would look like this:
function(doc) {
emit(doc.date, doc.water);
}
Every key/value pair emitted from the map function is added to an index which can be queried later in its entirety or by a range of keys (keys which in this case represent a date).
And if an average is required we would use the built-in _stats reducer. The Map and Reduce portions are expressed in a Design Document like this one: https://reader.cloudant.com/so37613808/_design/aggregate
The subsequent index allows us to get an aggregate across the whole data set with:
https://reader.cloudant.com/so37613808/_design/aggregate/_view/waterbydate
Dividing the sum by the count gives us an average.
We can use the same index to provide data grouped by keys too:
https://reader.cloudant.com/so37613808/_design/aggregate/_view/waterbydate?group=true
Or we can select a portion of the data by supplying startkey and endkey parameters:
https://reader.cloudant.com/so37613808/_design/aggregate/_view/waterbydate?startkey=%222016-01-01%22&endkey=%222016-06-03%22
See https://docs.cloudant.com/creating_views.html for more details.