# Merit Skimmer¶

The fermipy-merit-skimmer script can be used to create skimmed Merit files (either MC or data) and serves as a replacement for the web-based merit skimmer tool. The script accepts as input a sequence of Merit file paths or lists of Merit file paths which can be either local (nfs) or xrootd.

$fermipy-merit-skimmer merit_list.txt --output=merit.root --selection='FswGamFilter' \ --aliases=aliases.yaml$ fermipy-merit-skimmer merit_list.txt --output=merit-clean.root \
--selection='FswGamFilter && CLEAN' --aliases=EvtClassDefs_P8R2.xml


where merit_list.txt is a text file with one path per line. The --selection option sets the selection that will be applied when filtering events in each file. The --output option sets the path to the output merit file. The --aliases option can be used to load an alias file (set of key/value cut expression pairs). This option can accept either a YAML alias file or an XML event class definition file. The following illustrates the YAML alias file format:

FswGamFilter : FswGamState == 0
TracksCutFilter : FswGamState == 0 && TkrNumTracks > 0
CalEnergyFilter : FswGamState == 0 && CalEnergyRaw > 0


One can restrict the set of output branches with the --branches option which accepts an alias file or a YAML file containing a list of branch names. In the former case all branch names used in the given alias set will be extracted and added to the list of output branches.

$fermipy-merit-skimmer merit_list.txt --output=merit.root --selection='FswGamFilter' \ --aliases=EvtClassDefs_P8R2.xml --branches=EvtClassDefs_P8R2.xml  One can split the skimming task into separate batch jobs by running with the --batch option. This will subdivide task into N jobs when N is the number of files in the list divided by --files_per_job. The name of the output ROOT file of each job will be appended with the index of the job in the sequence (e.g. skim_000.root, skim_001.root, etc.). The --time and --resources options can be used to set the LSF wallclock time and resource flags. $ fermipy-merit-skimmer merit_list.txt --output=merit.root --selection='SOURCE && FRONT' \
--branches=EvtClassDefs_P8R2.xml --files_per_job=1000 --batch --aliases=EvtClassDefs_P8R2.xml


When skimming MC files it can be useful to extract the jobinfo for tracking the number of thrown events. The --extra_trees option can be used to copy one or more trees to the output file in addition to the Merit Tuple:

\$ fermipy-merit-skimmer merit_list.txt --output=merit.root --extra_trees=jobinfo