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Reference Guide
pyroot001_arrayInterface.py
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## \file
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## \ingroup tutorial_pyroot
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## \notebook -nodraw
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## This tutorial illustrates the conversion of STL vectors and TVec to numpy
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## arrays without copying the data.
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## The memory-adoption is achieved by the dictionary __array_interface__, which
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## is added dynamically to the Python objects by PyROOT.
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##
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## \macro_code
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## \macro_output
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##
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## \date April 2018
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## \author Stefan Wunsch
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import
ROOT
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from
sys
import
exit
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try
:
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import
numpy
as
np
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except
:
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exit()
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# Create a vector ROOT object and assign values
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# Note that this works as well with a TVec
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vec = ROOT.std.vector(
"float"
)(2)
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vec[0] = 1
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vec[1] = 2
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print(
"Content of the ROOT vector object: {}"
.format([x
for
x
in
vec]))
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# Interface ROOT vector with a numpy array
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array = np.asarray(vec)
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print(
"Content of the associated numpy array: {}"
.format([x
for
x
in
array]))
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# The numpy array adopts the memory of the vector without copying the content.
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# Note that the first entry of the numpy array changes when assigning a new
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# value to the first entry of the ROOT vector.
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vec[0] = 42
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print(
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"Content of the numpy array after changing the first entry of the ROOT vector: {}"
.
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format([x
for
x
in
array]))
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# Use numpy features on data of ROOT objects
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print(
"Mean of the numpy array entries: {}"
.format(np.mean(array)))
tutorials
pyroot
pyroot001_arrayInterface.py
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