Can uproot3 write TBranches containing arrays?

Question

In uproot 3 documentation there is information, that uproot can write only branches containing 1 value per entry. On the other hand, I can see some topics on uproot Github regarding writing jagged arrays, etc. So, I would like to make sure: can uproot write TBranches containing arrays to a TTree? If so, is it documented anywhere?

Thanks!

Answer 1

This will be better documented when it's ported to Uproot 4, but the best documentation we have on writing jagged arrays in Uproot 3 right now is the pull request and associated issues (all linked to each other):

https://github.com/scikit-hep/uproot3/pull/477

Here is an example from the tests:

import uproot3
import awkward0

a = awkward0.fromiter([[0],
                       [1, 2],
                       [10, 11, 12]])

with uproot3.recreate(filename, compression=None) as f:
    f["t"] = uproot3.newtree({
        "branch": uproot3.newbranch(numpy.dtype(">i4"), size="n")
    })
    f["t"].extend({"branch": a, "n": [1, 2, 3]})

f = ROOT.TFile.Open(filename)
tree = f.Get("t")
for i, event in enumerate(tree):
    assert(numpy.all([x for x in event.branch] == a[i]))