How to obtain diagonal elements of the matrix in R

Question

I have a dataset as attached herewith.

I want to extract diagonal elements from this matrix. The output should look like below. How do I go about it using R?

Please find the link to the excel file.

https://1drv.ms/x/s!AmU_Vk1czmwRgWFvnMYsga56vVMb

Output of dput(df):

X X1 X2 X3 X4 X5 X6  X7 X8 X9 X10
1  11  1 12  4 46 78 45  89 45 45   7
2  12  2 56  5 12 12 23 566 26  6    
3  13  3 23 23 28 24 28  23 23       
4  14  4 45 12 26 46 24  12          
5  15  5 89 56 24 68 27              
6  16  6 23 26 26 78                 
7  17  8 23 24 24                    
8  18  9 12 27                       
9  19 12 45                          
10 20 56


structure(list(X = 11:20, X1 = c(1L, 2L, 3L, 4L, 5L, 6L, 8L, 
9L, 12L, 56L), X2 = c("12", "56", "23", "45", "89", "23", "23", 
"12", "45", " "), X3 = c("4", "5", "23", "12", "56", "26", "24", 
"27", " ", " "), X4 = c("46", "12", "28", "26", "24", "26", "24", 
" ", " ", " "), X5 = c("78", "12", "24", "46", "68", "78", " ", 
" ", " ", " "), X6 = c("45", "23", "28", "24", "27", " ", " ", 
" ", " ", " "), X7 = c("89", "566", "23", "12", " ", " ", " ", 
" ", " ", " "), X8 = c("45", "26", "23", " ", " ", " ", " ", 
" ", " ", " "), X9 = c("45", "6", " ", " ", " ", " ", " ", " ", 
" ", " "), X10 = c("7", " ", " ", " ", " ", " ", " ", " ", " ", 
" ")), row.names = c(NA, -10L), class = "data.frame")

Answer 1

I would reverse the order of the columns - then you can convert it to a matrix and take the diagonal easily:

df[ncol(df):1] %>% 
  as.matrix() %>% 
  diag()

or equivalently if you're not familiar with the pipe operator (%>%):

diag(as.matrix(df[ncol(df):1]))