Looping randomly inside a sample

ROOT
1

Hi again

I am re-writing my post as for some reason was deleted while being moved from the Root-Documentation to this thread

I am doing some pseudo and using TRandom3 for creating a list of events to be run over every time for every pseudo… The problem is that as my sample is large , it takes a lot of time to create this “index”… So, is there any other way to randomly loop inside a root file and read events except this method ?

Thanks in advance!

2

Hi,

[quote=“Alkass”]I am doing some pseudo and using TRandom3 for creating a list of events to be run over every time for every pseudo… The problem is that as my sample is large , it takes a lot of time to create this “index”… So, is there any other way to randomly loop inside a root file and read events except this method ?
[/quote]

If your events are stored in a tree/chain, then all you need to know (for each sample) is the maximum number of events. Then you can just pick the right number of random events (e.g., int indexOfRandomEvent = gRandom->Uniform (totalNumberOfEvents;) and get them.

I’ve used this technique often and it works well.

Cheers,
Charles