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pyroot001_arrayInterface.py File Reference

## Namespaces | |

namespace | pyroot001_arrayInterface |

This tutorial illustrates the conversion of STL vectors and TVec to numpy arrays without copying the data.

The memory-adoption is achieved by the dictionary **array_interface**, which is added dynamically to the Python objects by PyROOT.

import ROOT

from sys import exit

try:

import numpy as np

except:

exit()

# Create a vector ROOT object and assign values

# Note that this works as well with a TVec

vec = ROOT.std.vector("float")(2)

vec[0] = 1

vec[1] = 2

print("Content of the ROOT vector object: {}".format([x for x in vec]))

# Interface ROOT vector with a numpy array

array = np.asarray(vec)

print("Content of the associated numpy array: {}".format([x for x in array]))

# The numpy array adopts the memory of the vector without copying the content.

# Note that the first entry of the numpy array changes when assigning a new

# value to the first entry of the ROOT vector.

vec[0] = 42

print(

"Content of the numpy array after changing the first entry of the ROOT vector: {}".

format([x for x in array]))

# Use numpy features on data of ROOT objects

print("Mean of the numpy array entries: {}".format(np.mean(array)))

Content of the ROOT vector object: [1.0, 2.0]

Content of the associated numpy array: [1.0, 2.0]

Content of the numpy array after changing the first entry of the ROOT vector: [42.0, 2.0]

Mean of the numpy array entries: 22.0

- Date
- April 2018

Definition in file pyroot001_arrayInterface.py.