convert a matrix to a tidy data frame (from wide to long format as described in the tidyverse concept)
mat2df(x)a data.frame in long format with the 'value' column stores the original values and 'row' and 'col' columns stored in row and column index as in x
x <- matrix(1:15, nrow = 3)
mat2df(x)
#> value row col
#> 1 1 1 1
#> 2 2 2 1
#> 3 3 3 1
#> 4 4 1 2
#> 5 5 2 2
#> 6 6 3 2
#> 7 7 1 3
#> 8 8 2 3
#> 9 9 3 3
#> 10 10 1 4
#> 11 11 2 4
#> 12 12 3 4
#> 13 13 1 5
#> 14 14 2 5
#> 15 15 3 5