Be-A-Computer: Dictionaries

The purpose of these problems is to allow you to test your understanding of dictionaries. They should not take more than an hour to complete.

You should do these warm-up exercises by hand. We provide files that will allow you to check your answers.

To get started, run git pull upstream master to make sure you have the latest files. You can check your answers by running the Python program dictionaries.py in pp/bac/

Both warm-up exercises and the challenge exercise use the following constants and data:

(DATE, TICKER, OPEN, CLOSE) = (0, 1, 2, 3)

stocks = [['Date', 'Ticker Symbol', 'Open', 'Close'],
          ['2010-11-09', 'AMD', '8.22', '7.91'],
          ['2010-11-09', 'GOOG', '630.00', '624.82'],
          ['2010-11-09', 'QQQ', '53.95', '54.26'],
          ['2010-11-10', 'AMD', '8.22', '8.72'],
          ['2010-11-10', 'BSB', '620.00', '630.40'],
          ['2010-11-10', 'GOOG', '630.00', '630.40'],
          ['2010-11-10', 'QQQ', '53.95', '53.45'],
          ['2010-11-11', 'AMD', '8.22', '8.40'],
          ['2010-11-11', 'GOOG', '630.00', '634.82'],
          ['2010-11-11', 'QQQ', '53.95', '53.45']]

Warm-up exercise #1: What is the output of the following code?

def f1(data):
    d = {}
    for row in data[1:]:
        ticker = row[TICKER]
        if (float(row[CLOSE]) - float(row[OPEN])) < 0:
            d[ticker] = d.get(ticker, 0) + 1
    return d

print("Warmup exercise 1:")
print(f1(stocks))
print()

Warm-up exercise #2: What is the output of the following code?

def f2(data, threshold):
    d = {}
    for row in data[1:]:
        date = row[DATE]
        ticker = row[TICKER]
        spread = float(row[CLOSE]) - float(row[OPEN])
        if threshold <= spread:
            if date not in d:
                d[date] = []
            d[date].append(ticker)
    return d

print("Warmup exercise 2:")
print(f2(stocks, 0))
print()

Challenge exercise: What is the output of the following code?

def f3(data):
    d = {}
    for row in data[1:]:
        date = row[DATE]
        ticker = row[TICKER]
        close = float(row[CLOSE])
        if date not in d:
            d[date] = [close, [ticker]]
        elif d[date][0] < close:
            d[date] = [close, [ticker]]
        elif d[date][0] == close:
            d[date][1].append(ticker)
    return d

print("Challenge exercise:")
print(f3(stocks))
print()