vo004_SortAndSelect.py File Reference

Namespaces
namespace	vo004_SortAndSelect

Detailed Description

In this tutorial we learn how elements of an RVec can be easily sorted and selected.

 
import ROOT
from ROOT.VecOps import RVec, Argsort, Take, Sort, Reverse
 
# RVec can be sorted in Python with the inbuilt sorting function because
# PyROOT implements a Python iterator
v1 = RVec("double")(3)
v1[0], v1[1], v1[2] = 6, 4, 5
v2 = sorted(v1)
print("Sort vector {}: {}".format(v1, v2))
 
# For convenience, ROOT implements helpers, e.g., to get a sorted copy of
# an RVec ...
v2 = Sort(v1);
print("Sort vector {}: {}".format(v1, v2))
 
# ... or a reversed copy of an RVec.
v2 = Reverse(v1);
print("Reverse vector {}: {}".format(v1, v2))
 
# Helpers are provided to get the indices that sort the vector and to
# select these indices from an RVec.
v2 = Argsort(v1)
print("Indices that sort the vector {}: {}".format(v1, v2))
 
v3 = RVec("double")(3)
v3[0], v3[1], v3[2] = 9, 7, 8
v4 = Take(v3, v2)
print("Sort vector {} respective to the previously determined indices: {}".format(v3, v4))
 
# Take can also be used to get the first or last elements of an RVec.
v2 = Take(v1, 2)
v3 = Take(v1, -2)
print("Take the two first and last elements of vector {}: {}, {}".format(v1, v2, v3))
 
# Because the VecOps helpers return a copy of the input, you can chain the operations
# conveniently.
v2 = Reverse(Take(Sort(v1), -2))
print("Sort the vector {}, take the two last elements and reverse the selection: {}".format(v1, v2))

Sort vector { 6.0000000, 4.0000000, 5.0000000 }: [4.0, 5.0, 6.0]
Sort vector { 6.0000000, 4.0000000, 5.0000000 }: { 4.0000000, 5.0000000, 6.0000000 }
Reverse vector { 6.0000000, 4.0000000, 5.0000000 }: { 5.0000000, 4.0000000, 6.0000000 }
Indices that sort the vector { 6.0000000, 4.0000000, 5.0000000 }: { 1, 2, 0 }
Sort vector { 9.0000000, 7.0000000, 8.0000000 } respective to the previously determined indices: { 7.0000000, 8.0000000, 9.0000000 }
Take the two first and last elements of vector { 6.0000000, 4.0000000, 5.0000000 }: { 6.0000000, 4.0000000 }, { 4.0000000, 5.0000000 }
Sort the vector { 6.0000000, 4.0000000, 5.0000000 }, take the two last elements and reverse the selection: { 6.0000000, 5.0000000 }

Date

August 2018

Author

Stefan Wunsch

Definition in file vo004_SortAndSelect.py.