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Computed columns

scan --expr adds a derived column to the projection. It uses the same expression language as --where, but instead of a yes/no cut it produces a value per row.

hipoq scan rec.hipo --bank REC::Particle --cols pid --expr p --expr theta_deg
 event  row  pid   p       theta_deg
 0      0    11    2.36    12.4
 0      1    2212  1.07    18.9
 ...

Each --expr is either a NAME=EXPRESSION or a bare preset name. Repeat the flag for several columns.

Custom expressions​

hipoq scan rec.hipo --bank REC::Particle --expr "mt=sqrt(px*px+py*py)"
hipoq scan rec.hipo --bank REC::Particle --expr "logp=log(sqrt(px*px+py*py+pz*pz))"

The scanned bank is the expression's driver, so:

  • bare columns (px, pid) bind to the scanned bank, and
  • cross-bank references resolve by pindex.

Computed columns are data, so they appear in every output format (table, csv, ndjson, json) — not just the human table.

Presets​

A bare word is looked up as a preset. The physics presets follow CLAS12 REC::Particle conventions (angles in radians unless _deg):

PresetExpression
psqrt(px*px+py*py+pz*pz)
ptsqrt(px*px+py*py)
thetapolar angle, radians
theta_degpolar angle, degrees
phiazimuth, radians
phi_degazimuth, degrees
esqrt(p² + pdg_mass(pid)²)
sampling_fractionREC::Calorimeter.energy / p (cross-bank sum)
total_cal_energyREC::Calorimeter.energy (cross-bank sum)
hipoq scan rec.hipo --bank REC::Particle --cols pid \
  --expr p --expr theta_deg --expr sampling_fraction

sampling_fraction and total_cal_energy are cross-bank: on a REC::Particle scan they sum each particle's calorimeter rows via pindex, so they only make sense when a REC::Calorimeter bank is present.

Reverse gather​

Because the scanned bank is the driver, scanning a detector bank lets you pull the associated particle's columns — the gather direction of the pindex link:

# each calorimeter hit annotated with its particle's pid
hipoq scan rec.hipo --bank REC::Calorimeter --cols energy,sector \
  --expr "pid=REC::Particle.pid"

Here REC::Particle.pid, evaluated on a calorimeter row, reads the pid of the particle that row points at — the inverse of the summing you get when scanning REC::Particle.

Non-finite values

An expression that produces NaN or Inf (e.g. log of a negative, or a divide-by-zero) renders as an empty / null cell rather than aborting the scan.