Row-level merging of similar arrays

[artlbv]

(I have not really found a solution here but happy to update the issue otherwise)

I have two awkward arrays, e.g. barrel electrons and endcap electrons -> the same objects with the same variables/fields.

barrel_eles = [[{pt: 43.8, eta: -0.532}, {pt: 39.5, eta: 0.271}, ... [{pt: 11.5, eta: 0.951}]]
endcap_eles = [[], [{pt: 68.8, eta: 1.92}, {pt: 38, eta: 1.6}]]

I want to merge them such that for each row/event I get the concatenated list of objects, e.g.

merge_ele = ak..(barrel_eles, endcap_eles)
...
pt: <Array [[43.8, 39.5, 6], [68.8, 38, 11.5]] type='2 * var * float32'>
eta: <Array [[-0.532, 0.271, ... 1.6, 0.951]] type='2 * var * float32'>

Is there any built in method in awkward for this?

p.s. I made the above examples by splitting a single array by a criterion (abs(eta) < 1.5)

[ianna]

@artlbv - I think, you can get barrel_eles.pt and endcap_eles.pt as contents to make a ak.contents.UnionArray. I wonder why is it needed to separate pt and eta?

>>> barrel = ak.Array([[{"pt": 43.8, "eta": -0.532}, {"pt": 39.5, "eta": 0.271}], [{"pt": 11.5, "eta": 0.951}]])
>>> endcap = ak.Array([[], [{"pt": 68.8, "eta": 1.92}, {"pt": 38, "eta": 1.6}]])
>>> l1 = ak.to_layout(barrel.pt)
>>> l2 = ak.to_layout(endcap.pt)
>>> index = ak.index.Index64([0,1,0,1])
>>> tags = ak.index.Index8([np.int8(0),np.int8(0), np.int8(1),np.int8(1)])
>>> union = ak.contents.UnionArray(tags, index, contents={l1, l2})
>>> arr = ak.Array(union)
>>> arr
<Array [[43.8, 39.5], [11.5], ..., [68.8, 38]] type='4 * union[var * float6...'>

[agoose77]

@artlbv I think what you're asking for is provided by ak.concatenate, with the axis=1 argument:

import awkward as ak

barrel_eles = ak.from_iter([[{"pt": 43.8, "eta": -0.532}, {"pt": 39.5, "eta": 0.271}], [{"pt": 11.5, "eta": 0.951}]])
endcap_eles = ak.from_iter([[], [{"pt": 68.8, "eta": 1.92}, {"pt": 38, "eta": 1.6}]])

result = ak.concatenate((barrel_eles, endcap_eles), axis=1)

Under the hood, this will build a union like @ianna demonstrates, but this union will be erased as both arrays barrel_eles and endcap_eles have mergeable (the same!) types.

[artlbv]

thanks so much! (in the end it was that easy!)