The diag() function in R

r

Solution

You can use the functions `row` and `col` to find the indices where the column number is identical to the row number:

row(M) == col(M)
#       [,1]  [,2]  [,3]
# [1,]  TRUE FALSE FALSE
# [2,] FALSE  TRUE FALSE
# [3,] FALSE FALSE  TRUE

M[row(M) == col(M)]
# [1] 1 5 9

Problem

Is there a way to use the `diag()` function in a Matrix without using the built-in function or iteration? ``` M<-matrix(1:9, ncol=3) # make a matrix q5b<-function(M){ #function } ``` I know that `M[1,1]`, `M[2,2]`, and `M[3,3]` will give me the same output as `diag(M)`. However, I can't think of a way to do this without a for loop. My thought process was I should have a condition where `row index == column index` in the Matrix then print that value. I appreciate any suggestions.

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