如何平均对多个Firebase子节点进行投票？ [英] How to average votes over a number of Firebase child nodes?

问题描述

这个问题已经被问过了，但我不太明白答案。 / p>

我需要计算来自Firebase的数据数组的平均值，所以我有两个步骤。 b $ b

检索所有数据

确定同一数据中有多少条目

计算平均值

我的代码：

$ p $ myDataRef.orderByChild（ （child_added，function（snapshot）{
votes = snapshot.val（）。vote;
//console.log （投票值：+票）
}）;
$ b myDataRef.orderByChild（time）。startAt（time-180000）.endAt（time）.on（value，function（snapshot）{
numberOfVotes = snapshot.numChildren ）;
//console.log(Number of Votes：+ numberOfVotes）
}）;

函数calculateAverage（numberOfVotes，votes）{
return eval（votes.join（'+'））/ numberOfVotes;


console.log（calculateAverage）


我错误地解释了一些超级基本的东西，因为我无法弄清楚如何将Firebase查询中的数据取出并转换为函数。我缺少什么？

解决方案

Firebase异步加载数据。你只能确定你的平均数据查询完成加载完全。

一个想到的方法是：

  myDataRef.orderByChild（time）。startAt（time-180000）.endAt（time）.on（value，function ）{
 var voteCount = snapshot.numChildren（）; 
 var total = 0; 
 snapshot.forEach（function（voteSnapshot）{
 total + = voteSnapshot.val（）。投票; 
））; 
 console.log（Average =+ total / voteCount）; 
}）; 
  

有些注意事项：

• 我使用一个值事件。不知道为什么你同时使用值和 child_added ，但它似乎只是复杂的事情。 b $ b

也可以在收听小孩_ 事件时保持运行的平均值，但是您会必须倾听所有人的意见。

  var total = 0，
 voteCount = 0; 
 query = myDataRef.orderByChild（time）。startAt（time-180000）.endAt（time）; 
 query.on（child_added，function（snapshot）{
 voteCount + = 1; 
 total + = snapshot.val（）。vote; 
 console.log（运行平均值：+ total / voteCount）; 
}）; 
 query.on（child_removed，function（snapshot）{
 voteCount  -  = 1; 
 total  -  = snapshot.val（）。vote; 
 console.log（运行平均值：+ total / voteCount）; 
}）; 
  

This question has been asked before but I didn't quite understand the answer.

I need to calculate the average of an array of data from Firebase, so I have two steps.

1. Retrieve all the data
2. Determine how many entries there are in that same data
3. Calculate the average

My code:

myDataRef.orderByChild("time").startAt(time-180000).endAt(time).on("child_added", function(snapshot) {
    votes = snapshot.val().vote;
    //console.log("Vote value:" + votes)
});

myDataRef.orderByChild("time").startAt(time-180000).endAt(time).on("value", function(snapshot) {
    numberOfVotes = snapshot.numChildren();
    //console.log("Number of Votes:" + numberOfVotes)
});

function calculateAverage(numberOfVotes, votes) {
    return eval(votes.join('+')) / numberOfVotes;
}

console.log(calculateAverage)

I think I'm misinterpreting something super basic because I can't figure out how to get the data "out" of the Firebase query and into a function. What am I missing?

解决方案

Firebase loads data asynchronously. You can only determine you average once the data the query has been loaded completely.

One way that comes to mind is:

myDataRef.orderByChild("time").startAt(time-180000).endAt(time).on("value", function(snapshot) {
    var voteCount = snapshot.numChildren();
    var total = 0;
    snapshot.forEach(function(voteSnapshot) {
        total += voteSnapshot.val().vote;
    });
    console.log("Average=" + total / voteCount);
});

Some things of note:

• I use a single value event. Not sure why you were using both value and child_added, but it only seemed to complicate things.

It is also possible to keep a running average while listening to child_ events, but you'll have to listen to all of them.

var total = 0, 
    voteCount = 0;
    query = myDataRef.orderByChild("time").startAt(time-180000).endAt(time);
query.on("child_added", function(snapshot) {
    voteCount += 1;
    total += snapshot.val().vote;
    console.log("Running average: "+total/voteCount);
});
query.on("child_removed", function(snapshot) {
    voteCount -= 1;
    total -= snapshot.val().vote;
    console.log("Running average: "+total/voteCount);
});

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