MapReduce Challenge - sort by non-key value

bucket_data

{
    "5af5c2c8144a11e28f9f001c14010046": {
        "category": "clothing",
        "available": 20,
        "pricefrom": 180.0,
        "title": "2-Pack Heart Top",
        "created": 1350032036,
        "lastUpdated": 1351691717
        }
    },
    "4bce12d2121a11e2934a001c14010046": {
        "category": "clothing",
        "available": 1,
        "pricefrom": 1270.52,
        "title": "Tiger Coffee Travel Bag",
        "created": 1353511317,
        "lastUpdated": 1353511317
        }
    },
    "827dc48c12bd11e2994e001c14010046": {
        "category": "clothing",
        "available": 1,
        "pricefrom": 596.2,
        "title": "Cagua Carry All Bag",
        "created": 1353411297,
        "lastUpdated": 1353511297
        }
    },
}

gistfile1.txt

Question: How do change the reduce phase to sort (forward or backwards) on the lastUpdated timestamp array column?

mapreduce_keyanddate.py

import riak
import pprint

# Connect to riak
client = riak.RiakClient(host='127.0.0.1', port=8087, prefix='riak', transport_class=riak.RiakPbcTransport)
query = client.add('test_products')  # Set the bucket
arg = {"category": "clothing"} # set the argument

query.map("""
function(v, meta, arg) {
    var data = JSON.parse(v.values[0].data);
    if (arg.category == data.category) {
        return [[v.key, data.lastUpdated]];
    } else {
        return []
    }
}""", {"arg": arg})
query.reduce("function(v, arg) { return v.sort(); }")
products = query.run()
if products is None:
    products = []

pprint.pprint(products)

mapreduce_keyonly.py

import riak
import pprint

# Connect to riak
client = riak.RiakClient(host='127.0.0.1', port=8087, prefix='riak', transport_class=riak.RiakPbcTransport)
query = client.add('test_products')  # Set the bucket
arg = {"category": "clothing"} # set the argument

query.map("""
function(v, meta, arg) {
    var data = JSON.parse(v.values[0].data);
    if (arg.category == data.category) {
        return [v.key];
    } else {
        return []
    }
}""", {"arg": arg})
query.reduce("function(v, arg) { return v.sort(); }")
products = query.run()
if products is None:
    products = []

pprint.pprint(products)

Answer:

query.reduce("""
    function(v, arg) { return v.sort(
         function(x,y){
             return y[1] - x[1];
         }
    );
}""")