Taking an Average in CouchDB

More fun with CouchDB, this time taking an average of something:

// map
function(doc){
    emit(null, doc.info.size) // in place of doc.info.size, you'd put whatever
                               // value you want averaged here
}
// reduce
function(keys, values, rereduce) {
    if (!rereduce){
        var length = values.length
        return [sum(values) / length, length]
    }else{
        var length = sum(values.map(function(v){return v[1]}))
        var avg = sum(values.map(function(v){
            return v[0] * (v[1] / length)
            }))
        return [avg, length]
    }
}

The end result will be 2 values, the first is the average, the second is the total number of values that we took an average of. Phew! Who woulda thought taking an average would be so involved!