Combinations within an array of p4 vectors #107
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Hi, I have an array of p4 vectors and I am trying to calculate the DeltaR between all vectors in the array. I build the array like this: for each event in a ROOT file. For now, there are exactly 6 entries in the array but this may vary later. The output is a list of these arrays. Then, I try to find the combinations of pairs but I get an error when running the following code:
The error is as follows: Any advice on how to handle this? Thank you! |
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Replies: 1 comment 8 replies
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The default If I'm interpreting the data type correctly, Instead of putting this inside an event loop, collect all your data as lists of vectors in all events (one list per event). Then call Here's an example of doing that without having to create a bunch of Python objects (which use a lot of memory). It uses ak.ArrayBuilder: builder = ak.ArrayBuilder()
for event in events:
sixb_pt = event["sixb_pt"] # however you get these from the events
sixb_eta = event["sixb_eta"]
sixb_phi = event["sixb_phi"]
with builder.list():
for pt, eta, phi in zip(sixb_pt, sixb_eta, sixb_phi):
with builder.record("Momentum4D"): # not MomentumObject4D
builder.field("pt"); builder.real(pt)
builder.field("eta"); builder.real(eta)
builder.field("phi"); builder.real(phi)
signal_p4 = builder.snapshot()
combos = ak.combinations(signal_p4, 2)
lefts, rights = ak.unzip(combos)
deltaRs = lefts.deltaR(rights)(The name of the record type is not "MomentumObject4D" because it is not a Python object.) |
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I think I should mention that |
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If installing the behaviors globally, I just noticed that your pip uninstall awkward awkward1 uproot-methods uproot uproot4 # repeatedly, until there are none left
pip install awkward uproot # if you need uprootand import them without qualification: import awkward as ak # no "1"
import uproot # no "4"Edit: To directly answer your question, yes, there's only one Python type for all Awkward Arrays, regardless of the type of data they contain. So |
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Alright, so I did a cleanse and I think it was a step in the right direction! I now see that
However, I am getting this error now:
So for some reason, it thinks I am trying to use azimuthal coordinates despite entering "pt," "eta," and "phi." Any ideas about what's going on here? Thank you!! |
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The azimuthal coordinates that it is (and should be) looking for are "pt" and "phi". It's not finding them because it's calling "from_fields" instead of "from_momentum_fields," which recognizes "pt" as a synonym for "rho". The line numbers in your stack trace don't line up with the latest version of the code—what version are you using? I'm looking at the changes since the last released version, and there are quite a few, including one about Awkward Array and momentum synonyms (#84). It may be that we've been fixing bugs and just not releasing. I just released 0.8.2; try that. |
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That did it! I wiped uproot and awkward again but originally, I hadn't wiped vector. So I wiped all three (just in case) and reinstalled them and now it works! Thanks so much for the suggestion! I really appreciate your time and energy! |
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The default
axisfor ak.combinations is 1 because a typical use-case is lists of particles per event. I don't think that's the data type you're building—sincesignalconsists of records ({"pt": pt, "eta": eta, "phi": phi, "mass": mass}) and not lists of records,axis=1is beyond the depth of this array.If I'm interpreting the data type correctly,
axis=0would work for this array, but the idea is not to find all combinations of particles in a single event, it's to find all combinations of particles in all events, with a single function call.Instead of putting this inside an event loop, collect all your data as lists of vectors in all events (one list per event). Then call
ak.combinations…