Experience with using ROOT for final ATLAS data analysis steps

Most of the ATLAS analyses do their final step by processing TTree-based ntuples. As actual analysis selection optimisations take place at this step, it is crucial that one can process all events in a timely fashion. A (personal) experience writing a set of ROOT-based algorithms to process ntuples and create final histograms will be presented. More than 2 TB of data can be processed in about half a day with the help of simple parallelisation using different distributed computing infrastructures. The results can be used for the final publication plots.