r - Dimension Does Not Match When Populating Matrix

Question

I am currently working in R and I am trying to populate a matrix with a some for loops. However, I keep getting the "number of items to replace is not a multiple of replacement length" error. The way I set my matrix() is that I specified nrow (because I am sure of the size) and I leave the ncol blank.

How can I create a matrix that dynamically allocate the dimensions?

Any recommendations? Thank you.

Answer 1

A couple of options spring to mind:

• Make an informed guess as to the size of the matrix and allocate accordingly. Then have your code check to see if you would exceed the limits chosen and expand the object. If you expand by a reasonable chunk size (i.e. don't add just 1 column, add 10 or 20 or n depending on the size of your problem, whatever is reasonable) then you won't incur the copy/expand overhead that often, which is what bogs loops down if written badly.

• Store the data/result in a list, each component of which would be one row of your matrix. That way you fill in the object as you go along, and then can either process the resulting list into a matrix with padding, or just work directly with the list. If each row can be of a different length (number of columns) then it doesn't make sense to store as a matrix in the first place and the list is the better option.