RDataFrame Display ignores nRows if Count was used on that dataframe

[apetukho]

Dear ROOT experts,

I wanted to have a display of a subset of a RDataFrame but at the same time have the event count of the whole RDataFrame. However, if I call Count() on RDataFrame the Display() calls ignore nRows argument and prints the whole RDataFrame instead. Here’s a quick reproducer

import ROOT

df = ROOT.ROOT.RDataFrame(10).Define("x", "gRandom->Rndm()")
count = df.Count()
display = df.Display("x", 5)
display.Print()

it outputs

+-----+------------+
| Row | x          | 
+-----+------------+
| 0   | 0.99974175 | 
+-----+------------+
| 1   | 0.16290988 | 
+-----+------------+
| 2   | 0.28261781 | 
+-----+------------+
| 3   | 0.94720108 | 
+-----+------------+
| 4   | 0.23165654 | 
+-----+------------+
| 5   | 0.48497361 | 
+-----+------------+
| 6   | 0.95747696 | 
+-----+------------+
| 7   | 0.74430534 | 
+-----+------------+
| 8   | 0.54004366 | 
+-----+------------+
| 9   | 0.73995298 | 
+-----+------------+

I get the expected result from Dislpay() if I don’t use the Count()

import ROOT

df = ROOT.ROOT.RDataFrame(10).Define("x", "gRandom->Rndm()")
display = df.Display("x", 5)
display.Print()

+-----+------------+
| Row | x          | 
+-----+------------+
| 0   | 0.99974175 | 
+-----+------------+
| 1   | 0.16290988 | 
+-----+------------+
| 2   | 0.28261781 | 
+-----+------------+
| 3   | 0.94720108 | 
+-----+------------+
| 4   | 0.23165654 | 
+-----+------------+

Why does the Count() affects the result of the Display()? Is there a way around it?

Best regards,
Aleksandr

---

ROOT Version: 6.26/06
Platform: Ubuntu 20.04
Compiler: Precompiled

---

[vpadulan]

Dear @apetukho ,

This is a duplicate of Display does not respect parameters if another operation is booked before printing · Issue #11390 · root-project/root · GitHub. As you can see, the issue was already closed a while ago. Please update your ROOT version accordingly.

Cheers,
Vincenzo

[vpadulan]

@apetukho

ROOT.ROOT.RDataFrame

Also, there’s no need to repeat ROOT.ROOT twice in general