Need help to get data from Root file

[elizaveta]

Hello,I have a file with a lot of trees and need to get data from it as a text file.Who have experience in such kind of work?I can connect you by email or smth and send file.

[eguiraud]

Hi @elizaveta,
see e.g. my reply here.

Hope this helps!
Enrico

[elizaveta]

Thanks for your answer.I looked at tutorials,but didnt understand anything

[eguiraud]

At a very basic level, in C++ you can use the following:

ROOT::RDataFrame df("treename", "filename.root");
df.Foreach(someProcessingFunction, {"column1", "column2", "column3"});

where someProcessingFunction is any C++ function that takes three arguments of the type of column1, column2 and column3 in your dataset.

That’s probably the simplest C++ recipe for processing ROOT data, and someProcessingFunction could e.g. print the contents of the columns to standard output so that you can put them in a text file.

@swunsch might be able to suggest something as simple for Python.

Hope this helps!
Enrico

[swunsch]

Hi there,

In case you are familiar with the scipy software stack, here namely numpy and pandas, the most convenient way is probably the following snippet (it’s fully runnable, feel free to try!):

# Load the ROOT data as numpy arrays
import ROOT
df = ROOT.RDataFrame('TreeS', 'http://root.cern/files/tmva_class_example.root')
npy = df.AsNumpy(['var1', 'var2', 'var3'])

# Print the numpy arrays
print(npy)

# Make a pandas dataframe
import pandas
pdf = pandas.DataFrame(npy)

# Print the dataframe
print(pdf)

# Save them as a csv file
pdf.to_csv('data.csv')

Best
Stefan

[Axel]

And a word of warning: exporting to text files is usually not what you want. You should rather learn the tools at hand; Excel is rarely the answer