Complement of RVec Take operation

What is the best way to Take from an RVec when one has the list of indices that one doesn’t want to keep?

In my particular case I have three collections per event: pt, eta, phi, corresponding to kinematic properties of some generic particles. The goal is select the pt of the particles that are not part of the particle pair with the largest invariant mass. I would appreciate input here to ensure I am doing it as efficiently as possible.

My approach has been to first define the invariant masses column:

df.Define("M_pair",[](ROOT::RVec<double>& pt, ROOT::RVec<double>& eta, ROOT::RVec<double>& phi) {
        auto c = Combinations(pt,2);
        auto m  = ROOT::RVec(pt.size(),0.); // take particles to be massless
        return InvariantMasses(Take(pt,c[0]),Take(pt,c[1]),


Then I am selecting the highest mass and selecting the pt of the other particles like this:

.Define("other_pt",[](ROOT::RVec<double>& pt,ROOT::RVec<double>& masses) {

        auto c = Combinations(pt,2);
        auto max_M_pair = Reverse( Argsort( masses ) )[0];
        return pt[ (Combinations(pt,1)[0]!=c[0][max_M_pair] && Combinations(pt,1)[0]!=c[1][max_M_pair]) ];

I feel like this is second part is a bit clunky. Is there a better way to do what I want with vector operations?


@eguiraud, our RDataFrame expert is currently on vacation. I’m sure he’ll reply once back. If it’s really urgent, just let me know, I can try to find someone else…

It can wait!

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I hear you :slight_smile:

So basically you’d need RemoveAt(pt, max_M_pair)?

That can be added!

yes I think so. Well, its sort of the complement of Take , although I dont know if you think Leave is too unclear in terms of describing what it does.

Implemented here:

I expect it to be soon in master and nightly builds. You can also just copy-paste the implementation in your own code to have it available, it’s just a few lines.

EDIT: for future visitors, the feature will be part of v6.26