Copy a container from an AOD file to another

[panagiotis_bellos]

Dear root experts,

I need to copy a container from an AOD file and paste it in a DAOD file. The DAOD file comes from the specific AOD (has the same number of events), however this container was omitted my mistake during the derivation. I was wondering if there is any easy way to move it, just for a short file with few events to do some tests.

thank you,
Panagiotis

[Danilo]

Dear Panagiotis,

Welcome back: thanks for posting.

If I understand correctly, a slim analysis format has been derived from a more complete one but a column has been forgotten in the derivation configuration.
These things are painful but happen.
I see two options, roughly:

1. You have at disposal both the AOD and DAOD and you opt for a “two files solution”, where you go through both datasets after adding the column of the tree stored in the AOD in the DAOD. You won’t be reading the entire AOD, just one column of course, however you’ll have to deal with more files than the ones relative to the DAOD dataset.
2. You do 1. and snapshot the result in a third dataset, in order to avoid to read too many files.

It really depends on the boundary conditions of the problem, which could be related to many factors such as dictionaries needed to read the collection and so on.

Do you have a minimal reproducer, say made of 2 files with a few events each?

Cheers,
D