Upper triangle of a matrix to a vector by row

Say we want to get a square matrix into a vector. We can do:

to.upper<-function(X) X[upper.tri(X,diag=TRUE)]

but this will give us our upper triangular matrix as a vector by column, i.e.:

> X
       [,1]   [,2]   [,3]   [,4]   [,5]
[1,] -0.329 -0.825 -0.906  0.834  0.702
[2,]  1.195 -0.237 -1.132 -0.827  0.150
[3,] -0.097 -1.270 -1.397  0.450  0.791
[4,]  0.883 -0.574  1.538 -2.632  0.135
[5,]  1.993 -0.520 -0.071  0.094 -0.064
> to.upper(X)
[1] -0.329 -0.825 -0.237 -0.906 -1.132 -1.397  0.834 -0.827  0.450 -2.632  0.702  0.150  0.791  0.135 -0.064

If we want to get our upper triangular matrix as a vector by row (as I did), we can use:

to.upper<-function(X) t(X)[lower.tri(X,diag=TRUE)]

which works just as we'd hoped, i.e.:

> X
       [,1]   [,2]   [,3]   [,4]   [,5]
[1,] -0.329 -0.825 -0.906  0.834  0.702
[2,]  1.195 -0.237 -1.132 -0.827  0.150
[3,] -0.097 -1.270 -1.397  0.450  0.791
[4,]  0.883 -0.574  1.538 -2.632  0.135
[5,]  1.993 -0.520 -0.071  0.094 -0.064
> to.upper(X)
[1] -0.329 -0.825 -0.906  0.834  0.702 -0.237 -1.132 -0.827  0.150 -1.397  0.450  0.791 -2.632  0.135 -0.064

(Note that if we have a symmetric matrix than the upper triangular matrix by row & the lower triangular matrix by column are the same. Here I used a non-symmetric square matrix so that we could tell these apart.)