Example: Accessing Vantage SQL Function with SQLAlchemy - Teradata Package for Python

In this example, you calculate the standard average of column 'gpa' and 'admitted' of the "admissions_trains" dataset using the avg/average/ave function in Vantage.

Avg(value_expression)

• Create connection to Vantage and load example dataset.

  # Get the connection to the Vantage using create_context()
  >>> from teradataml import *
  >>>td_context = create_context(host=getpass.getpass("Hostname: "), username=getpass.getpass("Username: "), password=getpass.getpass("Password: "))
  

  # Load the example dataset.
  load_example_data("GLM", ["admissions_train"])

• Prepare example dataset.

  # Create the DataFrame on 'admissions_train' table
  >>> admissions_train = DataFrame("admissions_train")
  >>> admissions_train

     masters   gpa     stats programming  admitted
  id                                              
  13      no  4.00  Advanced      Novice         1
  9       no  3.82  Advanced    Advanced         1
  33      no  3.55    Novice      Novice         1
  6      yes  3.50  Beginner    Advanced         1
  7      yes  2.33    Novice      Novice         1
  22     yes  3.46    Novice    Beginner         0
  37      no  3.52    Novice      Novice         1
  35      no  3.68    Novice    Beginner         1
  27     yes  3.96  Advanced    Advanced         0
  4      yes  3.50  Beginner      Novice         1

• Import func module from SQLAlchemy package.

  # Import func from SQLAlchemy to use the same for executing aggregate functions
  >>> from sqlalchemy import func

• Use the func module to generate a function object "agg_func_".

  >>> agg_func_ = func.avg(admissions_train.gpa.expression)
  

  Where:
  • func: sqlalchemy module that is imported.
  • avg: the Vantage function name.
    The function name is case insensitive.

    You can pass the function name in lowercase (avg), uppercase (AVG) or in mixed cases (Avg).

  • admissions_train.gpa.expression: an expression that is passed to the function, specifying the column to use for calculating average.

    Where:

    admissions_train: the teradataml DataFrame;

    gpa: a column name of the teradataml DataFrame;

    Together, admissions_train.gpa forms a ColumnExpression (teradataml DataFrame Column).

    expression: a property of teradataml DataFrame column, which is passed as the required expression to this function object.

• View the type of the function object "agg_func_".

  >>> type(agg_func_)

  sqlalchemy.sql.functions.Function

• Pass the function object "agg_func_", with other function objects for calculating average value of the 'admitted' column, to DataFrame.assign() function.

  >>> df = admissions_train.assign(True, avg_gpa_=agg_func_, average_admitted_=func.average(admissions_train.admitted.expression), ave_admitted_=func.ave(admissions_train.admitted.expression))
  
  >>> print_variables(df, ["avg_gpa_", "average_admitted_", "ave_admitted_"])

  Equivalent SQL: select ave(admitted) AS ave_admitted_, average(admitted) AS average_admitted_, avg(gpa) AS avg_gpa_ from "admissions_train"
  
  
   ************************* DataFrame ********************* 
     ave_admitted_  average_admitted_  avg_gpa_
  0           0.65               0.65   3.54175
  
  
  
   ************************* DataFrame.dtypes ********************* 
  ave_admitted_        float
  average_admitted_    float
  avg_gpa_             float
  
  
  
   'avg_gpa_' Column Type: FLOAT
   'average_admitted_' Column Type: FLOAT
   'ave_admitted_' Column Type: FLOAT

  Different function names "AVERAGE" and "AVE" that Vantage offers to calculate average are used along with 'avg'.
  "print_variables()" is a private function used to display example outputs here. This function uses "DataFrame.show_query()" to print the query, "print(dataframe)" to display dataframe content, and "DataFrame.dtypes" to display DataFrame column types. This function is not part of the teradataml package.