How can i group a the elements of a Matrix and returns an aggregation function in SQL style?

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Luigi Treccozzi 2018-7-15

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评论： Luigi Treccozzi 2018-7-15

Hi guys! I'll show you an example of what I'd like to do: I have a matrix A

A = [

1 2 3

2 1 2

1 2 6

2 1 4

]

Suppose I want to group by the first two columns and return for each of those the mean value of the third column. The output matrix will be

A_group = [

1 2 4.5

2 1 3

]

Is there any function that implements such a functionality? Thanks

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Rik 2018-7-15

I don't understand your question, but if you already have the sum, can't you just divide that by the number of elements?

Luigi Treccozzi 2018-7-15

I don't know what that number is before I aggregate. I thought at this solution but I don't know how can I count them. Anyway, my question is: How can I aggregate some rows in a matrix? Look at the example. Of course I have some more complex matrix on which to work

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