Pandas array to TGraph

ROOT
1

Dears rooters,

I’m having a problem to create a TGraph from pandas dataframe.
This is the part of the code, where I read the data with pandas, I convert the 2 columns in array in order to pass them to the TGraph:

import pandas as pd
df=pd.read_csv(csv_off, sep=’\t’)

n= len(df[‘HV1’])
x= df[‘HV1’].values
y= df[‘EFF1’].values

w= TGraph(n,x,y)

canvas= TCanvas()
w.Draw(“APE”)

canvas.SaveAs(“p.png”)

The error that I got is:
Error in <TGaxis::PaintAxis>: length of axis is 0

I check the data reading and it is ok

thanks in advance

2

Hi,

not sure what the cause could be. Anyway, perhaps the best solution would be to use RDataFrame directly in ROOT:

import ROOT
MakeCsvDataFrame = ROOT.ROOT.RDF.MakeCsvDataFrame
# here it depends if you have headers for your columns or not
hasHeaders=false
df = MakeCsvDataFrame("myTextInput", hasHeaders, "\t")
# again here we assume you do not have headers
g = df.Graph("Col0", "Col1")
canvas= ROOT.TCanvas()
g.Draw(“APE”)
canvas.SaveAs(“p.png”)

Cheers,
D