RDataFrame Min function does not compile

Newbie
,
1

Hello,

I can not compile the Min() function in the RDataFrame class (Max() works by the way…)

I attach test.py (574 Bytes) a simple macro where you can see the problem. Here is the result on lxplus:

python -i test.py
min= In file included from /builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/input_line_12:15:
In file included from /builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/etc/dictpch/allHeaders.h:973:
In file included from /builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/include/ROOT/RCsvDS.hxx:14:
In file included from /builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/include/ROOT/RDataFrame.hxx:20:
In file included from /builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/include/ROOT/RDF/RInterface.hxx:15:
/builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/include/ROOT/RDF/ActionHelpers.hxx:734:24: error: no matching function for call to ‘min’
fMins[slot] = std::min(v, fMins[slot]);
^~~~~~~~
/builddir/build/BUILD/root-6.22.02/x86_64-redhat-linux-gnu/include/ROOT/RDF/RAction.hxx:237:33: note: in instantiation of function template specialization ‘ROOT::Internal::RDF::MinHelper::Exec<ROOT::VecOps::RVec, 0>’ requested here

Thank you for your help.

     Tancredi

_ROOT Version: root-6.22.02/
_Platform: lxplus
_Compiler: x86_64-redhat-linux-gnu

2020-09-23T22:00:00Z

2

Hi,
I’m not sure why the error message is so obscure. When I try to execute your script, with ROOT 6.22.02 installed via conda, here’s what I get:

~/Downloads python -i test.py                                                                                                                                                                         (root-6-22-02) 
Traceback (most recent call last):
  File "test.py", line 18, in <module>
    print('min= ',df["data"].Min("photon_eta[0]").GetValue())
cppyy.gbl.std.runtime_error: Template method resolution failed:
  ROOT::RDF::RResultPtr<double> ROOT::RDF::RInterface<ROOT::Detail::RDF::RLoopManager,void>::Min(basic_string_view<char,char_traits<char> > columnName = "") =>
    runtime_error: Unknown column: photon_eta[0]
  ROOT::RDF::RResultPtr<double> ROOT::RDF::RInterface<ROOT::Detail::RDF::RLoopManager,void>::Min(basic_string_view<char,char_traits<char> > columnName = "") =>
    runtime_error: Unknown column: photon_eta[0]

And indeed the problem is that Min("photon_eta[0]") should be e.g. Define("ph_eta0", "photon_eta[0]").Min("ph_eta0"): actions like Min only accept column names, they don’t know how to evaluate expressions such as "photon_eta[0]" (Define can be used to evaluate expressions).

Cheers,
Enrico

3

Hello,

yes this work.

I had started the investigation with
print 'min= ',df[“data”].Min(“photon_eta”).GetValue()
print 'max= ',df[“data”].Max(“photon_eta”).GetValue()

The MAX work while the MIN gives the same error as about.

Regards,
Tancredi

1 Like
4

Ok I see the problem, this is now https://github.com/root-project/root/issues/6435 . Work in progress.

5

Hi again, the bug is understood and a fix is in the pipeline.

In Python, I can suggest to use Stats instead of Min/Max to work around the issue:

stats = df["data"].Stats("photon_eta").GetValue()
min = stats.GetMin()
max = stats.GetMax()

Cheers,
Enrico

6

The fix will be in ROOT v6.24 and v6.22/04. Thanks for the report!