Bool_t not supported in `AsMatrix`

Dear experts,
I am trying to read a TTree in PyROOT, and convert it into an array.
I am using the function AsMatrix() provided by the TTree class, but as soon as I try to include a branch which contains Bool_t values, I get the following error

*** Exception: Reading of branch ['truth_matched'] is not supported (branch has unsupported data-type ['Bool_t']).

Is there any way to circumvent this problem?
Thanks in advance

_ROOT Version: 6.16
_Platform: SLC6
Compiler: Not Provided

Hi @simeloni,

AFAIK, the pythonization for TTree does not support Bool_t. Other than that, @etejedor may know of a workaround, if any. Unfortunately, he is off until April.


@swunsch can also probably help here. I think you could create a snapshot of the tree where you convert the bool to a float value.




Best solution is AsNumpy with support for boolean values :slight_smile: Indeed, booleans in this context are evil, the memory layout in numpy arrays (1 byte per bool) and in std::vector (1 bit per bool) makes quite some complications.

However, try this!

import ROOT
import numpy as np

# Create some data on the fly with RDataFrame, plug in your own dataset!
# - a float column
# - a boolean column
# - an integer column (created from the boolean column, potentially preferred and more efficient)
df = ROOT.RDataFrame(5) \
         .Define('some_float', 'float(rdfentry_)') \
         .Define('some_bool', 'rdfentry_ > 2') \
         .Define('some_int', 'int(some_bool)')

# Move the data to numpy arrays
data = df.AsNumpy(['some_float', 'some_bool', 'some_int'])

# Optional: Make a matrix of floats out of it
matrix = np.vstack((data[col] for col in data)).astype(np.float)
 'some_float': ndarray([0., 1., 2., 3., 4.], dtype=float32),
 'some_bool': ndarray([False, False, False, True, True], dtype=object),
 'some_int': ndarray([0, 0, 0, 1, 1], dtype=int32)
[[0. 1. 2. 3. 4.]
 [0. 0. 0. 1. 1.]
 [0. 0. 0. 1. 1.]]


Dear all,
thanks for your help! Indeed as @swunsch said, the best idea would be to use AsNumpy. Problem is that we are bound (from analysis needs) to ROOT v6.16, which does not have support for this, afaik.

@moneta, yes I think that would work, but would be a bit slow for our needs, since we are dealing with huge datasets. The solution I have found is similar in fact: I create a new branch in the DataFrame, converting the bool into a int, and then I snapshot just this new additional branch. Later on, I define this additional tree as friend, and use the new branch, that now works in AsMatrix.

It is a bit cumbersome, but practical. If you have any other solution which is compatible with the above constraints, please share it :wink: .


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