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This script lives in /reg/g/psdmsdf/group/lcls/ds/ana/tutorials/examplePython3psana1_examples/randomAccess.py and demonstrates how to jump to a specific event using the three "timestamp" numbers that uniquely identify an LCLS event: seconds/nanoseconds/fiducials (fiducials increment at 360Hz and repeat every ~20 minutes, the other two numbers are a standard unix seconds/nanoseconds timestamp). In LCLS-II there will be only one number that will identify an event.
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from psana import *
ds = DataSource('exp=xpptut15:run=54:smd')
# LCLSLCLS1 uses 3 numbers to define an event. In LCLS2 this willis be one number.
seconds = []
nanoseconds = []
fiducials = []
# get some times of events (these could come from a saved "small data" file, for example)
for nevent,evt in enumerate(ds.events()):
evtId = evt.get(EventId)
seconds.append(evtId.time()[0])
nanoseconds.append(evtId.time()[1])
fiducials.append(evtId.fiducials())
if nevent==2: break
# now that we have the times, jump to the events in reverse order
ds = DataSource('exp=xpptut15:run=54:idx')
runmyrun = next(ds.runs().next()
for sec,nsec,fid in zip(reversed(seconds),reversed(nanoseconds),reversed(fiducials)):
et = EventTime(int((sec<<32)|nsec),fid)
evt = runmyrun.event(et)
print(evt.get(EventId).fiducials()) |
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from psana import *
ds = DataSource('exp=xpptut15:run=54:idx')
run = next(ds.runs().next()
times = run.times()
print(f'Found {len(times)} events in run')
for nevt, t in enumerate(times):
evt = run.event(t)
if nevt==2:
break |
...
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