apply statement applied to a 2x3 matrix gives an error when used with a function

[mmarion]

OUTPUT:
tableStats (class=list)

[[1]]
[,1] [,2] [,3]
[1,] 170 30 0.1500000
[2,] 59 86 0.4068966

[[2]]
[,1] [,2] [,3]
[1,] 0.000000 0.000000 0.00000000
[2,] 2.828427 2.828427 0.01950639

[[3]]
[,1] [,2] [,3]
[1,] 0 0 0.0000000
[2,] 2 2 0.0137931

OUTPUT:
mean.mat (class=matrix or array)
[,1] [,2] [,3]
[1,] 170 30 0.1500000
[2,] 59 86 0.4068966

dim(mean.mat)  =  2 3

Error2.f <- function(mat)
1 - sum(diag(mat[,1:2]))/sum(mat[,1:2])

apply(mean.mat,1:2,Error2.f)

Error in mat[, 1:2] : incorrect number of dimensions
Why is this not operating on first two columns of mean.mat?

Thanks. M

[nirgrahamuk]

your apply says to take each cell in turn MARGINS=c(1,2) and apply a function that expects a matrix input ; but its not a matrix input, its a scalar value, the value of a cell of your matrix input

[mmarion]

I am not sure how to fix this. rewrite error function or refer to matrix differently.

[nirgrahamuk]

We would have to know what your intentions are in order to best advise you

[mmarion]

matrix .mat is a 2x3 matix
I want to work on only first 2 columns ; let's call it matrix2
Then I want to compute error rate using function seen in the code.

Doing it this way allows for computing the error rate for a matrix of three variables (matrix3).
matrix3 <- {a b c, d e f,g h i}.
I have not worked with such a problem but it seems reasonable that off diagonal elements are components of misclassification.

Latest try:

mean.mat

output:
[,1] [,2] [,3]
[1,] 151.94878 28.05122 0.1559543
[2,] 55.23124 75.26876 0.4234487

error.rate.f <- function(mat){
1- sum(diag(mat))/sum(mat)}
apply(mean.mat, 1:2, error.rate.f)

        [,1]        [,2] [,3]

[1,] 0.006244078 0.001825946 1
[2,] 0.004186761 0.003570671 1

Desired output: error rate = (28.05122+55.23124)/345. = .24140

I need to understand what is going on here. 1:2 seems to be a problem in the apply statement but I don't know what to change it to?

M

[nirgrahamuk]

Is it your intention to use the error function once, or multiple times ? If once you dont need to use apply at all.

[mmarion]

I will want to use error function multiple times.

[nirgrahamuk]

With respect to the single 2x3 matrix ? Then, if
If so, which subsets would you wish to apply it to ?

[mmarion]

I would like to apply it to the 4 cells with indices 11,12,21,22 leaving column with indices 13,23 unmodified or removed

[nirgrahamuk]

(m1 <- matrix(c(151.94878, 28.05122 ,0.1559543,
55.23124, 75.26876 ,0.4234487), ncol = 3,byrow = TRUE))

(subset_of_interest <- m1[1:2,1:2])

error.rate.f <- function(mat){
  1- sum(diag(mat))/sum(mat)}

error.rate.f(subset_of_interest)

[mmarion]

Subsetting is exactly what I wanted to do. I was getting confused with the 1:2 referring to rows and columns of the subsetted matrix and the 1:2 in the apply statement.

I'm finding the apply statement to be confusing but I'm continuing to work at its interpretation.

Thank you very much.
M