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-% !TEX program = xelatex
-\documentclass{article}
-\usepackage{../style}
-\usepackage{disclaimer}
-\usepackage{../langs}
-
-
-
-\begin{document}
-
-\section*{Core Part 6 (Scala, 7 Marks)}
-
-\IMPORTANT{This part is about Scala. It is due on \cwSIXa{} at 4pm and worth 7\%.}
-
-\noindent
-Also note that the running time of each part will be restricted to a
-maximum of 30 seconds on my laptop.
-
-\DISCLAIMER{}
-
-\subsection*{Reference Implementation}
-
-Like the C++ assignments, the Scala assignments will work like this: you
-push your files to GitHub and receive (after sometimes a long delay) some
-automated feedback. In the end we take a snapshot of the submitted files and
-apply an automated marking script to them.\medskip
-
-\noindent
-In addition, the Scala coursework comes with a reference implementation
-in form of \texttt{jar}-files. This allows you to run any test cases
-on your own computer. For example you can call Scala on the command
-line with the option \texttt{-cp drumb.jar} and then query any
-function from the template file. Say you want to find out what
-the functions ???
-produce: for this you just need to prefix them with the object name
-\texttt{CW6b}.
-If you want to find out what these functions produce for the argument
-\texttt{6}, you would type something like:
-
-\begin{lstlisting}[language={},numbers=none,basicstyle=\ttfamily\small]
-$ scala -cp collatz.jar
-
-scala> CW6a.collatz(6)
-...
-scala> CW6a.collatz_max(6)
-...
-\end{lstlisting}%$
-
-\subsection*{Hints}
-
-\noindent
-\textbf{For Core Part:} useful string functions:
-\texttt{.startsWith(...)} for checking whether a string has a given
-prefix, \texttt{\_ ++ \_} for concatenating two strings; useful option
-functions: \texttt{.flatten} flattens a list of options such that it
-filters way all \texttt{None}'s, \texttt{Try(...).getOrElse ...} runs
-some code that might raise an exception---if yes, then a default value
-can be given; useful list functions: \texttt{.head} for obtaining the
-first element in a non-empty list, \texttt{.length} for the length of
-a list; \texttt{.filter(...)} for filtering out elements in a list;
-\texttt{.getLines.toList} for obtaining a list of lines from a file;
-\texttt{.split(",").toList} for splitting strings according to a
-comma.\bigskip
-
-\noindent
-\textbf{Note!} Fortunately Scala supports operator overloading. But
-make sure you understand the difference between \texttt{100 / 3} and
-\texttt{100.0 / 3}!
-
-\newpage
-\subsection*{Core Part (7 Marks, file drumb.scala)}
-
-A purely fictional character named Mr T.~Drumb inherited in 1978
-approximately 200 Million Dollar from his father. Mr Drumb prides
-himself to be a brilliant business man because nowadays it is
-estimated he is 3 Billion Dollar worth (one is not sure, of course,
-because Mr Drumb refuses to make his tax records public).
-
-Since the question about Mr Drumb's business acumen remains open,
-let's do a quick back-of-the-envelope calculation in Scala whether his
-claim has any merit. Let's suppose we are given \$100 in 1978 and we
-follow a really dumb investment strategy, namely:
-
-\begin{itemize}
-\item We blindly choose a portfolio of stocks, say some Blue-Chip stocks
- or some Real Estate stocks.
-\item If some of the stocks in our portfolio are traded in January of
- a year, we invest our money in equal amounts in each of these
- stocks. For example if we have \$100 and there are four stocks that
- are traded in our portfolio, we buy \$25 worth of stocks
- from each. (Be careful to also test cases where you trade with 3 stocks.)
-\item Next year in January, we look at how our stocks did, liquidate
- everything, and re-invest our (hopefully) increased money in again
- the stocks from our portfolio (there might be more stocks available,
- if companies from our portfolio got listed in that year, or less if
- some companies went bust or were de-listed).
-\item We do this for 41 years until January 2019 and check what would
- have become out of our \$100.
-\end{itemize}
-
-\noindent
-Until Yahoo was bought by Altaba a few years ago, historical stock market
-data for such back-of-the-envelope calculations was freely available
-online. Unfortunately nowadays this kind of data is more difficult to
-obtain, unless you are prepared to pay extortionate prices or be
-severely rate-limited. Therefore this part comes with a number
-of files containing CSV-lists with the historical stock prices for the
-companies in our portfolios. Use these files for the following
-tasks.\bigskip
-
-\newpage
-\noindent
-\textbf{Tasks}
-
-\begin{itemize}
-\item[(1)] Write a function \texttt{get\_january\_data} that takes a
- stock symbol and a year as arguments. The function reads the
- corresponding CSV-file and returns the list of strings that start
- with the given year (each line in the CSV-list is of the form
- \texttt{someyear-01-someday,someprice}).\hfill[1 Mark]
-
-\item[(2)] Write a function \texttt{get\_first\_price} that takes
- again a stock symbol and a year as arguments. It should return the
- first January price for the stock symbol in the given year. For this
- it uses the list of strings generated by
- \texttt{get\_january\_data}. A problem is that normally a stock
- exchange is not open on 1st of January, but depending on the day of
- the week on a later day (maybe 3rd or 4th). The easiest way to solve
- this problem is to obtain the whole January data for a stock symbol
- and then select the earliest, or first, entry in this list. The
- stock price of this entry should be converted into a double. Such a
- price might not exist, in case the company does not exist in the given
- year. For example, if you query for Google in January of 1980, then
- clearly Google did not exist yet. Therefore you are asked to
- return a trade price with type \texttt{Option[Double]}\ldots\texttt{None}
- will be the value for when no price exists; \texttt{Some} if there is a
- price.\hfill[1 Mark]
-
-\item[(3)] Write a function \texttt{get\_prices} that takes a
- portfolio (a list of stock symbols), a years range and gets all the
- first trading prices for each year in the range. You should organise
- this as a list of lists of \texttt{Option[Double]}'s. The inner
- lists are for all stock symbols from the portfolio and the outer
- list for the years. For example for Google and Apple in years 2010
- (first line), 2011 (second line) and 2012 (third line) you obtain:
-
-\begin{verbatim}
- List(List(Some(312.204773), Some(26.782711)),
- List(Some(301.0466), Some(41.244694)),
- List(Some(331.462585), Some(51.464207))))
-\end{verbatim}\hfill[1 Mark]
-
-
-%\end{itemize}
-
-%\subsection*{Advanced Part 3 (4 Marks, continue in file drumb.scala)}
-%
-%\noindent
-%\textbf{Tasks}
-
-%\begin{itemize}
-
-\item[(4)] Write a function that calculates the \emph{change factor} (delta)
- for how a stock price has changed from one year to the next. This is
- only well-defined, if the corresponding company has been traded in both
- years. In this case you can calculate
-
- \[
- \frac{price_{new} - price_{old}}{price_{old}}
- \]
-
- If the change factor is defined, you should return it
- as \texttt{Some(change\_factor)}; if not, you should return
- \texttt{None}.\mbox{}\hfill\mbox{[1 Mark]}
-
-\item[(5)] Write a function that calculates all change factors
- (deltas) for the prices we obtained in Task (2). For the running
- example of Google and Apple for the years 2010 to 2012 you should
- obtain 4 change factors:
-
-\begin{verbatim}
- List(List(Some(-0.03573991804411003), Some(0.539974575389325)),
- List(Some(0.10103414222249969), Some(0.24777764141006836)))
-\end{verbatim}
-
- That means Google did a bit badly in 2010, while Apple did very well.
- Both did OK in 2011. Make sure you handle the cases where a company is
- not listed in a year. In such cases the change factor should be \texttt{None}
- (recall Task~(4)).
- \mbox{}\hfill\mbox{[1 Mark]}
-
-\item[(6)] Write a function that calculates the ``yield'', or
- balance, for one year for our portfolio. This function takes the
- change factors, the starting balance and the year as arguments. If
- no company from our portfolio existed in that year, the balance is
- unchanged. Otherwise we invest in each existing company an equal
- amount of our balance. Using the change factors computed under Task
- (2), calculate the new balance. Say we had \$100 in 2010, we would have
- received in our running example involving Google and Apple:
-
- \begin{verbatim}
- $50 * -0.03573991804411003 + $50 * 0.539974575389325
- = $25.21173286726075
- \end{verbatim}
-
- as profit for that year, and our new balance for 2011 is \$125 when
- converted to a \texttt{Long}.\mbox{}\hfill\mbox{[1 Mark]}
-
-\item[(7)] Write a function that calculates the overall balance
- for a range of years where each year the yearly profit is compounded to
- the new balances and then re-invested into our portfolio.
- For this use the function and results generated under (6).\\
- \mbox{}\hfill\mbox{[1 Mark]}
-\end{itemize}\medskip
-
-
-
-\noindent
-\textbf{Test Data:} File \texttt{drumb.scala} contains two portfolios
-collected from the S\&P 500, one for blue-chip companies, including
-Facebook, Amazon and Baidu; and another for listed real-estate
-companies, whose names I have never heard of. Following the dumb
-investment strategy from 1978 until 2019 would have turned a starting
-balance of \$100 into roughly \$39,162 for real estate and a whopping
-\$462,199 for blue chips. Note when comparing these results with your
-own calculations: there might be some small rounding errors, which
-when compounded lead to moderately different values.\bigskip
-
-
-\noindent
-\textbf{Moral:} Reflecting on our assumptions, we are over-estimating
-our yield in many ways: first, who can know in 1978 about what will
-turn out to be a blue chip company. Also, since the portfolios are
-chosen from the current S\&P 500, they do not include the myriad
-of companies that went bust or were de-listed over the years.
-So where does this leave our fictional character Mr T.~Drumb? Well, given
-his inheritance, a really dumb investment strategy would have done
-equally well, if not much better.\medskip
-
-\end{document}
-