Creating a matrix from a long data.frame
There can never be too many examples for transforming data with R. So, here is another example of reshaping a
data.frame into a
Here I have a data frame that shows incremental claim payments over time for different loss occurrence (origin) years.
The format of the data frame above is how this kind of data is usually stored in a data base. However, I would like to see the payments of the different origin years in rows of a matrix.
The first idea might be to use the
reshape function, but that would return a
data.frame. Yet, it is actually much easier with the
matrix function itself. Most of the code below is about formatting the dimension names of the matrix. Note that I use the
with function to save me a bit of typing.
An elegant alternative to
matrix provides the
acast function of the
reshape2 package. It has a nice formula argument and allows me not only to specify the aggregation function, but also to add the margin totals.