Merging arrays in uproot4

[claudiopascoal]

Hi,
My name is Cláudio, from the LZ collaboration.
i) I have two trees in which one is data and the second tree is Monte-Carlo.
ii) Then, from each tree I select only some branches and create a class 'awkward.highlevel.Array' in the following way:
arrays = tree1.arrays(variables)
iii) I would like to add Monte-Carlo branches to the arrays variables which contains data branches. Before, in uproot3, we could use:
arrays.update(tree2.arrays(mc_variables))
but this method is no longer available in uproot4.
What is the solution for this?

Thanks

[jpivarski]

Actually, this is an Awkward Array question, though I should start by saying that if you need to keep using Awkward 0/Uproot 3 for any reason, you can

pip install awkward0 uproot3

and these packages can be imported into the same Python session with the new libraries.

As for updating an array, there is this syntax:

arrays["new_field_name"] = new_field

and there's this, using ak.zip:

new_arrays = ak.zip({"field1": field1, "field2": field2, ...}, depth_limit=1)

Here's an example if you don't know or don't want to explicitly iterate over the fields using ak.unzip and ak.fields:

>>> a = ak.Array([{"a": 1}, {"a": 2}, {"a": 3}])
>>> bc = ak.Array([{"b": 1, "c": 1}, {"b": 2, "c": 2}, {"b": 3, "c": 3}])
>>> ak.zip(dict(zip(ak.fields(a), ak.unzip(a)), **dict(zip(ak.fields(bc), ak.unzip(bc)))))
<Array [{a: 1, b: 1, c: 1}, ... b: 3, c: 3}] type='3 * {"a": int64, "b": int64, ...'>

(New versions of Python have fancy syntax for merging dicts, but I'm using old syntax that's guaranteed to work.)

[claudiopascoal]

It works well, thanks!