# [SOLVED] Computational error while using combination function in R

## Issue

I have a matrix in `R`, namely `dat`, and I am trying to create a information matrix using the `infotheo` package between all variable combinations. This is the code:

``````set.seed(1234)
m <- 10
n <- 5
dat <- round(matrix(runif(m * n), m, n))

library(infotheo)
a = combn(seq(ncol(dat)), 2, function(x)condinformation(dat[, x], dat[,x], method = 'emp'))
b <- structure(a, Size = ncol(dat), class = 'dist')
b <- as.matrix(b)
``````

which result in the following:

``````> b
1           2          3          4           5
1 0.000000000 0.004021743 0.06326870 0.19497599 0.004021743
2 0.004021743 0.000000000 0.03218930 0.01384429 0.291103166
3 0.063268705 0.032189301 0.00000000 0.01384429 0.013844294
4 0.194975994 0.013844294 0.01384429 0.00000000 0.032189301
5 0.004021743 0.291103166 0.01384429 0.03218930 0.000000000
``````

My problem is that while all values are correct, i.e.,`condinformation(dat[, 1], dat[,2],method = 'emp')=0.004021743`, the diagonal elements are incorrect. For example

``````> condinformation(dat[, 1], dat[,1],method = 'emp')
 0.6108643
``````

what I am doing wrong in my code and get this result? Do you have an alternative solution for the desired outcome?

## Solution

As det mentioned, `combn` won’t do (1, 1), (2, 2), etc. Try this instead.

``````b <- matrix(0, n, n)
b[lower.tri(b, TRUE)] <- combn(seq(n + 1), 2, function(x) condinformation(dat[, x], dat[,x - 1], method = 'emp'))
b[upper.tri(b)] <- b[lower.tri(b)]
``````