Reading values from TLeaf containing vector<double> type data in PyROOT

ROOT
1

Hello everyone

I have a .root file that contains the structure as: TDirectory -> TTree -> TBranch -> TLeaf. Few TBranches contain only one TLeaf which contains data of type vector. I want to read the data using PyROOT. I have been able to access each leaf from this file structure. But, I am unable to read the vector data contained in the leaf. Can anyone guide or point me to some tutorial or code snippet from where I can get a solution to this?

Best regards

2

Hi,
From Python something like:

vector = file_name.tree_name.branch_name

should work if the branch with name branch_name contains the vector

Lorenzo

3

Thanks for the response. Will try that and update…

4

Hello

I tried what you had suggested but it doesn’t work as the .root file also contains a directory. When I do:
dir = file_name.directory_name
this works and I can see that dir is assigned the pointer to the directory. But it doesn’t work when I do:
tree = file_name.directory_name.tree_name
It throws an error:
AttributeError: 'TDirectoryFile' object has no attribute 'tree'

Shubham

5

Hi,
Please try:

file = TFile.Open("file_name.root")
tree = file.Get("dir_name/tree_name")
for event in tree:
   v = tree.branch_name
   ...
6

Hello

This I think iterates through the vector and returns the pointer to the vector as many times as the size of the vector.

<ROOT.vector<double> object at 0x5b5ef70>
<ROOT.vector<double> object at 0x5b5ef70>
<ROOT.vector<double> object at 0x5b5ef70>
<ROOT.vector<double> object at 0x5b5ef70>
<ROOT.vector<double> object at 0x5b5ef70>
.
.
.
.

So, I think this will work but I am unable to dereference the pointer and get the values.

7

This iterates over the entries of the tree and gets the vector branch value for every entry of the tree. When you are processing a particular entry of the tree, you can iterate over the values of the current vector or access particular positions of it:

file = TFile.Open("file_name.root")
tree = file.Get("dir_name/tree_name")
for event in tree:
   v = tree.branch_name
   for elem in v:
       print(elem)
   print(v[0])
1 Like
8

Hello

This worked. Thanks a lot. :slight_smile:

Best regards
Shubham

9

Hi

Just asking out of curiosity, is it possible to access the vector by passing a string to some function (like we did to get the tree in the previous line), instead of doing tree.branch_name? I mean something like:
v = tree.someGetFunction("branch_name")

10

Hi,
Yes, you can do getattr(tree, 'branch_name').
Cheers,
Enric

11

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