read the dataframe "global_dataframe" from csv file "Sum Dat.csv" get the absolute error between the columns "EVa" and "EVb" grouped by the column "TV" conserving the column "TV" transformed to string

def abs_error_by_tv(dataframe, string_tv):
  dataframe.loc[:,"error"] = dataframe.loc[:,"EVa"] - dataframe.loc[:,"EVb"]
  dataframe.loc[:,"error"] = abs(dataframe.loc[:,"error"])
  return dataframe.pivot_table(index = string_tv, values = "error")