pep-material: comparison cws/cw01.tex

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-:d58954a96ec1
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 \texttt{.sortBy(\_.\_2)} sorts a list of pairs according to the second
 elements in the pairs---the sorting is done from smallest to highest;
 useful \texttt{Map} functions: \texttt{.toMap} converts a list of
 pairs into a \texttt{Map}, \texttt{.isDefinedAt(k)} tests whether the
 map is defined at that key, that is would produce a result when
-called with this key.
+called with this key; useful data functions: \texttt{Source.fromURL},
+\texttt{Source.fromFile} for obtaining a webpage and reading a file.
 \newpage
 \subsection*{Advanced Part 3 (4 Marks)}
 have become out of our \$100.
 \end{itemize}
 \noindent
 Until Yahoo was bought by Altaba this summer, historical stock market
-data was available online for free, but nowadays this kind of data is
+data for such back-of-the-envelope calculations was available online
-difficult to obtain unless you are prepared to pay extortionate prices
+for free, but nowadays this kind of data is difficult to obtain, unless
-or be severely rate-limited.  Therefore this coursework comes with a
+you are prepared to pay extortionate prices or be severely
-number of files containing CSV-lists about stock prices of
+rate-limited.  Therefore this coursework comes with a number of files
-various companies. Use these files for the following tasks.\bigskip
+containing CSV-lists about historical stock prices for companies of
+our portfolio. Use these files for the following tasks.\bigskip
 \noindent
 \textbf{Tasks (file drumb.scala):}
 \begin{itemize}
 \item[(1.a)] Write a function \texttt{get\_january\_data} that takes a
-stock symbol and a year as argument. The function reads the
+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{year-01-someday,someprice}.
+\texttt{year-01-someday,someprice}).
 \item[(1.b)] Write a function \texttt{get\_first\_price} that takes
-again stock symbol and a year as arguments. It should return the
+again a stock symbol and a year as arguments. It should return the
-first January price for the stock symbol in the year. For this it
+first January price for the stock symbol in given the year. For this
-obtains the list of strings generated by
+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 entry in this list. This entry should
+and then select the earliest, or first, entry in this list. The
-be converted into a double.  Such a price might not exist, if the
+stock price of this entry should be converted into a double.  Such a
-company does not exist in the given year. For example, if you query
+price might not exist, in case the company does not exist in the given
-for Google in January of 1980, then clearly Google did not exists
+year. For example, if you query for Google in January of 1980, then
-yet.  Therefore you are asked to return a trade price as
+clearly Google did not exists yet.  Therefore you are asked to
-\texttt{Option[Double]}.
+return a trade price as \texttt{Option[Double]}\ldots\texttt{None}
+will be the value for when no price exists.
 \item[(1.c)] 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. You should organise this as a
+first trading prices for each year in the range. You should organise
-list of lists of \texttt{Option[Double]}'s. The inner lists are for
+this as a list of lists of \texttt{Option[Double]}'s. The inner
-all stock symbols from the portfolio and the outer list for the
+lists are for all stock symbols from the portfolio and the outer
-years.  For example for Google and Apple in years 2010 (first line),
+list for the years.  For example for Google and Apple in years 2010
-2011 (second line) and 2012 (third line) you obtain:
+(first line), 2011 (second line) and 2012 (third line) you obtain:
 \begin{verbatim}
 List(List(Some(311.349976), Some(27.505054)),
 List(Some(300.222351), Some(42.357094)),
 List(Some(330.555054), Some(52.852215)))
 List(List(Some(-0.03573992567129673), Some(0.5399749442411563))
 List(Some(0.10103412653643493), Some(0.2477771728154912)))
 \end{verbatim}
 That means Google did a bit badly in 2010, while Apple did very well.
-Both did OK in 2011.\hfill\mbox{[1 Mark]}
+Both did OK in 2011.\\
+\mbox{}\hfill\mbox{[1 Mark]}
 \item[(3.a)] 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
+received in our running example involving Google and Apple:
 \begin{verbatim}
 $50 * -0.03573992567129673 + $50 * 0.5399749442411563
 = $25.21175092849298
 \end{verbatim}
 as profit for that year, and our new balance for 2011 is \$125 when
 converted to a \texttt{Long}.
 \item[(3.b)] 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.\mbox{}\hfill\mbox{[1 Mark]}
+the new balances and then re-invested into our portfolio.\\
+\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 2017 would have turned a starting
-balance of \$100 into roughly \$30,895 for real estate and a whopping
+balance of \$100 into roughly \$30,839 for real estate and a whopping
-\$188,172 for blue chips.  Note when comparing these results with your
+\$349,597 for blue chips.  Note when comparing these results with your
-own results: there might be some small rounding errors, which when
+own calculations: there might be some small rounding errors, which
-compounded, lead to moderately different values.\medskip
+when compounded, lead to moderately different values.\bigskip
+\noindent
+\textbf{Hints:} useful string functions: \texttt{startsWith(...)} for
+testing a string having a given prefix, \texttt{\_ + \_} for
+concatenating twop 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.\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
 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
-\noindent
-\textbf{Hints:}
 \end{document}
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