Introduction

In this assignment you will write a class ColumnDict that takes a table in the form of a list of lists (e.g. from a CSV file) and provides a key-value data structure (dictionary) where the values are the columns of the table.

For full marks in this assignment your solutions should not use any loops, but only comprehensions (and other builtin functions as needed). Your solution should also work with arbitrarily large input.

Make sure you commit and push all your work using coursegit before 16:30 on Thursday November 27.

Dictionary functionality

Provide a constructor, and appropriate “dunder” methods so that the following tests pass. You should only store the data once.

def test_one_row():
    table= ColumnDict([["alice", "bob"],
                       [27, 32]])
    assert table["bob"] == [32]
    assert table["alice"] == [27]


def test_two_rows():
    table2= ColumnDict( [["alice", "bob"],
                         [1, 2],
                         [False, True]])
    assert table2["bob"] == [2,True]
    assert table2["alice"] == [1,False]

def test_three_cols():
    table3= ColumnDict( [["alice", "mallory", "bob"],
                         [1, 3, 2],
                         [False, None, True]])
    assert table3["bob"] == [2,True]
    assert table3["alice"] == [1,False]
    assert table3["mallory"] == [3,None]

def test_update():
      table3= ColumnDict( [["alice", "mallory", "bob"],
                           [1, 3, 2],
                           [False, None, True]])
      table3["bob"]=[42,False]
      assert table3["bob"] == [42,False]
      assert table3["alice"] == [1,False]
      assert table3["mallory"] == [3,None]

Selecting subsets of columns

Write a select method for you ColumnDict class that produces table (list of lists) table with subset of the columns. Your select method should handle any number of key arguments, including zero.

def test_select1():
   table3= ColumnDict( [["alice", "mallory", "bob"],
                        [1, 3, 2],
                        [False, None, True]])

   out=table3.select("alice", "mallory")
   assert out == [["alice", "mallory"],
                  [1, 3],
                  [False, None]]

def test_select2():
   table3= ColumnDict( [["alice", "mallory", "bob"],
                        [1, 3, 2],
                        [False, None, True]])

   assert table3.select() == []

Iterator

Provide appropriate dunder methods to support iteration. Do not copy or traverse the data more times than necessary. Do not use generators (i.e. yield). Your code should pass (at least) the following tests.

def test_iter1():
    rows= [["alice", "mallory", "bob"],
                         [1, 3, 2],
                         [False, None, True]]
    expected = [["alice", "bob", "mallory"],
                         [1, 2, 3],
                         [False, True, None]]
    table3= ColumnDict( rows )
    assert list(table3) == expected

def test_iter2():
    rows= [["alice", "mallory", "bob"],
                         [1, 3, 2],
                         [False, None, True]]
    expected = [["alice", "bob", "mallory"],
                         [1, 2, 3],
                         [False, True, None]]
    table3= ColumnDict( rows )
    out = []
    for row in table3:
        out.append(row)

    assert out == expected

def test_iter3():
    rows= [["alice", "mallory", "bob"],
           [1, 3, 2],
           [False, None, True]]
    expected = [["alice", "bob", "mallory"],
                [1, 2, 3],
                [False, True, None]]
    table3= ColumnDict( rows )
    assert [ row for row in table3 ] == expected
    assert list(table3) == expected