Thank you very much, this worked perfectly on the sample and my real data. I modified slightly by removing the notsorted option in the data step and including an explicit proc sort as below. proc sort data = have; by road carriage attribute1 start; run; For validation, I summed the lengths by various features in the original data set and compared to those in the end result, as well as a spot check of a random selection of roads. Thanks again for your time! ... View more

Thank you @FreelanceReinh . I feel a bit sick that I was ignorant of this! For now, I've used the ROUND function to two decimals throughout my data sets and now I'm off to read more on the issue! ... View more

Thanks @himalayan. This worked well, and I don't regularly use proc summary so it was nice to see an alternative method! It was however a bit slower to process than the SQL method, so have accepted that solution. ... View more