Underscore Aggregate Hashes by Keys - node.js

Question

I work on machine learning application. I use underscorejs when I need to operate with arrays and hashes.
The question is following, in ML there is a cross-validation approach, when you need to calculate performance for several folds.
For each fold, I have a hash of parameters of performance, like following
{ 'F1': 0.8,
'Precision': 0.7,
'Recall':0.9
}
I push all hashes to the array, at the end I have an array of the hashes, like following
[ { 'F1': 0.8,
'Precision': 0.7,
'Recall':0.9
},
{ 'F1': 0.5,
'Precision': 0.6,
'Recall':0.4
},
{ 'F1': 0.4,
'Precision': 0.3,
'Recall':0.4
}
]
The question is, at the end I want to calculate the average for each parameter of the hash, i.e. I want to sum up all hashes by parameters and then divide every parameters by the number of folds, in my case 3.
If there are any elegant way to do so with underscore and javascript?
One important point is sometimes I need to do this aggregation, when the hash for fold like the following
{
label1:{ 'F1': 0.8,
'Precision': 0.7,
'Recall':0.9
},
label2:{ 'F1': 0.8,
'Precision': 0.7,
'Recall':0.9
},
...
}
The task is the same, average of F1, Precision, Recall for every label among all folds.
Currently I have some ugly solution that run over all hash several times, I would appreciate any help, thank you.

Answer 1

If it is an array, just use the array. If it is not an array, use _.values to turn it into one and use that. Then, we can do a fold (or reduce) over the data:
_.reduce(data, function(memo, obj) {
return {
F1: memo.F1 + obj.F1,
Precision: memo.Precision + obj.Precision,
Recall: memo.Recall + obj.Recall,
count: memo.count + 1
};
}, {F1: 0, Precision: 0, Recall: 0, count: 0})
This returns a hash containing F1, Precision, and Recall, which are sums, and count, which is the number of objects. It should be pretty easy to get an average from those.