Review 2

General Questions

• What constitutes a good baseline? (Hint: See lecture notes on baselines)
  • Enumerate the categories and provide a one line description.
• What is a pareto frontier?
  • True/False -- There exists a pareto frontier for 1-objective problem
  • True/False -- An n-objective optimizer has an n-dimensional pareto frontier
• How does Naive Bayes work?
  • What are the merits and demerits
• What family of data mining methods would you use for these cases?

    No. classes |  Symbolic  | Numerics |
    ------------|------------|----------|--
    0           |            |          |
    ------------|------------|----------|--
    > 1         |            |          |
    ------------|------------|----------|--
    = 1         |            |          |
    ------------|------------|----------|--

• Discuss some strategies to obtain a class value while performing kNN for
  • A symbolic class (True or False)
  • A numeric class (where values falls between 0 to 1)
  • No class variable

        @relation weather

        @attribute outlook {sunny, overcast, rainy}
        @attribute temperature real
        @attribute humidity real
        @attribute windy {TRUE, FALSE}
        @attribute play {yes, no}

        @data
        sunny,85,85,FALSE,no
        sunny,80,90,TRUE,no
        overcast,83,86,FALSE,yes
        rainy,70,96,FALSE,yes
        rainy,68,80,FALSE,yes
        rainy,65,70,TRUE,no
        overcast,64,65,TRUE,yes
        sunny,72,95,FALSE,no
        sunny,69,70,FALSE,yes
        rainy,75,80,FALSE,yes
        sunny,75,70,TRUE,yes
        overcast,72,90,TRUE,yes
        overcast,81,75,FALSE,yes
        rainy,71,91,TRUE,no

Using the above example, answer the following questions:

• On variable types:
  • What is symbolic variables? Please give 2 examples.
  • What is numeric variables? Please give 2 examples.
  • Name one operation that can be performed on both numeric and symbolic variables.
  • Name one operation that can be performed on numeric but not symbolic variables.
  • How do you calculate the distance between symbolic variables? Please give 1 example.
  • How do you calculate the distance between numeric variables? Please give 1 example.
  • What is normalization? Why might it be useful?
  • In the above data, normalize temperature=65, humidity=70
• On Independent variables:
  • What is independent variable? Given an example
  • What's the difference between decision tree and random forest?
• On Impurity:
  • What is the connection between variance and standard deviation?
  • What is the same about variance and entropy?
  • What is difference between variane and entropy?
  • How do we calculate entropy? What is the entropy of play? Show your working.
  • How do we calculate standard deviation? What is the standard deviation of temperature? Show your working.
  • Note: The Gini Index is used to compute the impurity of a data partition. It is computed as 1 - (∑ (p.i)^2). For example, assume the data partition D consisiting of 4 classes each with equal probability. Then the Gini Index (Gini Impurity) will be: Gini(D) = 1 - (0.25^2 + 0.25^2 + 0.25^2 + 0.25^2)
  • Is Gini defined for symbolic or number variables?
• On Dependent variables:
  • Define a dependent variable. Given an example.
  • What the difference between supervised and unsupervised learning? Please give 2 example tasks for each of them.
  • In classification taskes, is the dependent variable numeric or symbolic? What about regressions?
  • If there are more than one numeric class variable, what kind of problem do we have?
• On Decision Tree learning:
  • Decision tree is often called "iterative dichomization". Why?
  • In the following decision tree, outlook is the top split and temperature never appears in the tree. Why could that be?
  • For the golf dataset above, do the following, show all your calculations and explainations:
    • calculate the entropy of the class variables.
    • calculate the expected value of the entropy of the class symbol after splitting on outlook.
    • calculate the expected value of the entropy of the class symbol after splitting on temperature.
    • compare the three values. What can you say?

    outlook = sunny
    |   humidity = high: no
    |   humidity = normal: yes
    outlook = overcast: yes
    outlook = rainy
    |   windy = TRUE: no
    |   windy = FALSE: yes

Python Stuff

• What is the airspeed velocity of an unladen swallow?
• What does yield do?
  • How is it different from a return?
• What is the purpose of a context manager?
• Given the following code, explain what happens with respect to context manager-

    with open(f, 'w') as fname:
        "do some thing"
        "do some more things"

• Match the following regex terms to their tasks fill-up-this
• Explain the following regex operation. Specfically, what happens to the string variable a_text_string in the following snippet-

        re.sub(r'([ \n\r\t]|#.* )', "", a_text_string)

• Give an example of a ternary operator in python.
• What does the enumerate operation do in python?
• Explain what's going on here-

        [a[i] for i, user in enumerate(users) if user==True]