MATLAB Accumarray加权平均值 [英] MATLAB Accumarray weighted mean

问题描述

因此，我目前正在使用"accumarray"来查找与匹配ID相对应的一系列数字的平均值.防爆输入:

So I am currently using 'accumarray' to find the averages of a range of numbers wich correspond to matching ID's. Ex Input:

ID----Value
1     215
1     336
1     123
2     111
2     246
2     851

我当前的代码使用ID作为分隔符"来找到上述值的未加权平均值，这样我就不会将所有值的平均值作为一个数字得到，而是将单独的结果仅作为有相应的ID. EX输出:

My current code finds the unweighted average of the above values, using the ID as the 'seperator' so that I don't get the average for all of the values together as one number, but rather seperate results for just values which have corresponding ID's. EX Output:

ID----Value
1     224.66
2     402.66

要实现这一点，我正在使用以下代码:

To achieve this I am using this code:

[ID, ~, Groups] = unique(StarData2(:,1),'stable');
app = accumarray(Groups, StarData2(:,2), [], @mean);

以StarData2作为函数的输入.到目前为止，这对于我的目的来说是完美的，我需要知道是否可以使accumarray为我提供加权平均值，以便可以为应用程序中的每个点(在找到平均值之前)分配一个权重，或者@mean可以被可以实现这一目标的功能所取代.新的输入将如下所示:

With StarData2 being the input of the function. This is working perfectly for my purposes until now, I need to know if accumarray can be made to give me a weighted average, such that each point in app (before the average is found) can be assigned a weight or that the @mean can be replaced with a function that can achieve this. The new input will look like this:

ID----Value----Weight
1     215     12
1     336     17
1     123     11
2     111     6
2     246     20
2     851     18

新代码必须执行sum(val(i)* weight(i))/sum(weight)，而不仅仅是标准均值.感谢您的协助.

The new code must do the sum(val(i)*weight(i))/sum(weight) instead of just the standard mean. Thanks for any assistance.

推荐答案

您可以将行索引用作"vals"( accumarray )，然后定义您自己的函数，该函数对数据组进行加权均值:

You can use the row index as the "vals" (second input to accumarray) and define your own function that does the weighted mean on group of the data:

Weights = data(:,3); Vals = data(:,2); % pick your columns here
WeightedMeanFcn = @(ii) sum(Vals(ii).*Weights(ii))/sum(Weights(ii));
wmeans = accumarray(Groups, 1:numel(Groups), [], WeightedMeanFcn)

---

演示

从data(带有权重的新输入)和unique命令开始:

Starting with data (the new input with your weights) and your unique command:

data = [1,215,12; 1,336,17; 1,123,11; 2,111,6; 2,246,20; 2,851,18];
[ID, ~, Groups] = unique(data(:,1),'stable');

accumarray用法如下(每次更改data时都要重新定义WeightedMeanFcn ！)

The accumarray usage is as follows (redefine WeightedMeanFcn every time you change data!):

>> Weights = data(:,3); Vals = data(:,2); % pick your columns here
>> WeightedMeanFcn = @(ii) sum(Vals(ii).*Weights(ii))/sum(Weights(ii));
>> app = accumarray(Groups, 1:numel(Groups), [], WeightedMeanFcn)
app =
  241.1250
  475.0909

与第一组一起手动检查:

Checking manually, with the first group:

ig = 1;
sum(data(Groups==ig,2).*data(Groups==ig,3))/sum(data(Groups==ig,3))
ans =
  241.1250

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