TChain like behavior?

[HDembinski]

tl;dr: It would be nice if the docs could elaborate a bit on how to best replace a TChain to process several files at once with uproot facilities. I found the note regarding lazyarrays, but I was wondering whether there is more.

I wanted to process several files in a TChain-like way with uproot. From the reading the docs it was not clear to me how achieve this. It seems like uproot.open can only open one file. I found the lazyarray(s), which are great, but I would still like to know whether TChain-like processing of several files is possible with uproot or not.

[HDembinski]

Ok, now I have read the full tutorial. Basically, what I want is uproot.iterate. So all that is needed then is an additional sentence in that section of the tutorial, that uproot.iterate is the closest to TChain-like processing.

[HDembinski]

If there is a sentence that mentions TChain explicitly, then the note can be found with ctrl+f

[jpivarski]

Since the interface is array-at-a-time, rather than event-at-a-time, there isn't a direct analogue, but most users replace TChain with uproot.iterate.

The unbound functions in the uproot namespace (as opposed to the bound methods of TTree) can operate on lists and globs of files. None of them automatically concatenate across files (except, in a sense, lazyarrays) because branches and types can differ, but awkward.concatenate can do that.

[jpivarski]

Good point. TODO: add a note about TChain in the readme.

[HDembinski]

One thing I find difficult with uproot.iterate is that I cannot apply event-level cuts on tracks, because the information is lost which tracks belong to which event. I will open another issue about this.