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I have a table created using the table() command in R:
y
x 0 1 2 3 4 5 6 7 8 9
0 23 0 0 0 0 1 0 0 0 0
1 0 23 1 0 1 0 1 2 0 2
2 1 1 28 0 0 0 1 0 2 2
3 0 1 0 24 0 1 0 0 0 1
4 1 1 0 0 34 0 3 0 0 0
5 0 0 0 0 0 33 0 0 0 0
6 0 0 0 0 0 2 32 0 0 0
7 0 1 0 1 0 0 0 36 0 1
8 1 1 1 1 0 0 0 1 20 1
9 1 3 0 1 0 1 0 1 0 24
This table shows the results of a classification, and I want to sum the leading diagonal of it (the diagonal with the large numbers - like 23, 23, 28 etc). Is there a sensible/easy way to do this in R?
221
b = trace( A ) calculates the sum of the diagonal elements of matrix A : tr ( A ) = ∑ i = 1 n a i i = a 11 + a 22 + ... + a n n .
The numbers that are diagonal to each other add up to make the same number because you're adding one that's lower or higher by 1, 2 or 3 to the number beside it. For example, in a 3x3 square, the number in the top right is 2 more than the number in the top left.
The elements of the leading diagonal of L are all ones so that . Since U is upper triangular, its determinant is the product of the elements of its leading diagonal. Thus, taking account of row interchanges the appropriately signed product of the diagonal elements of U gives the determinant.
How about sum(diag(tbl)), where tbl is your table?
140
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