Graphic display of portfolio stock values

Format Conversions

Because the dates are formatted yyyy/mm/dd, pofo has a dt_parse() function (line 226) to define the format and convert the date entries to DateTime objects. As an additional service, the cfg_read() function accepts a reference to the @symbols array, which it populates with all ticker symbols that occur, avoiding duplicates (lines 212-215).

The function returns a reference to the%by_date hash that it populates. The keys in this hash are date values in the form of stringified DateTime objects. The values are each mapped to an array of transactions that have taken place on the same days (line 217). In turn, each transaction comprises an array that contains the fields from the corresponding configuration file line – that is, date, action, ticker symbol, and the number of shares. Cash actions also occur here with cash as their ticker symbol.

To see how many shares of one stock the portfolio holds on a specific day, the script needs to work its way through the transactions that occurred in the portfolio up to this date. Therefore, the for loop starting in line 36 first works its way through all actions before the $start date. The hash keys are dates, which the sort command sorts in ascending order.

The loop calls the pos_add() function for each transaction and puts the results in the %pos hash. The hash assigns a numeric value to each ticker symbol in the portfolio. For shares, this is the number, and for cash, this is simply the sum. The second for loop starting in line 79 then does the same calculation for every single day after the start date, until the current date.

Share acquisitions and sales additionally trigger a movement in the cash item; new shares cost money, and the proceeds from selling shares are credited to the account. On every action, the daily share price is applied; the data is provided by CachedQuote.pm.

RRD Tool Abstract

The area graph for the individual items comes courtesy of RRDtool by Tobias Oetiker [1]. The object-oriented RRDTool::OO CPAN module helps to Perlify and elucidate the unusual syntax of this practical tool.

RRDtool stores data from RRD archives by cumulating the measuring points of one or more data sources. In predefined intervals, the so-called step size, an average is calculated. In line 62 of Listing 2, the pofo program sets the step parameter to 24 hours, telling the RRD database to expect just one update per day. The program assigns a separate data source to each stock (map() call in lines 65-72).

The RRD archive can store up to 5,000 values (line 74) before it starts to overwrite the values in typical RRD style. At a rate of one new value a day, it will take more than 10 years for this to happen. The GAUGE parameter in line 69 stipulates that RRDtool should accept the values directly and not cumulate them; however, RRDtool refuses to accept values for times prior to the last stored daily value; to cope with this, pofo deletes any remaining RRD files in line 55 and the RRDTool::OO constructor quickly recreates them.

Line 16 of Listing 2 defines a freely selectable color palette of RGB values. In lines 46-53, pofo selects a value for each share to be displayed from the @colors array, allowing the viewer to distinguish the stocks in the graph.

The %symbol_colors hash holds the symbol/color palette mappings. The order in which the actions occur in the configuration file defines the display order in the graph.

The for loop starting in line 79 works its way through the days to be displayed in the graph. Each time it does, the if condition in line 83 checks to see whether transactions are available for the current day and, if so, calls pos_add() to add them, thus ensuring that the global hash %pos contains the current portfolio configuration.

The sum_up() function then determines the daily balance of the portfolio and stores the cash values of the individual items in the %parts hash index by the share ticker keys (or cash). After this, the RRD object's update() method passes the hash in to the RRD database, applying the time stamp for the day that has just been processed (line 95). The graph() method finally draws the graph output in the positions.png file and writes the legend at the bottom edge of the image (lines 102-122). The listing shown here only uses six colors for shares, but nothing prevents you from adding new colors to the @colors array in lines 16-18.

In lines 31-34, pofo sets the display period to two years in the past until today. You can change this by modifying the $start and $end variables. If you prefer more information on what is going on during the data processing state, just uncomment line 13; easy_init() then initializes Log4perl, and the output from the DEBUG instructions spread liberally throughout the source code will be directed onto your screen.

The script has no concept of stock splits, in which the historic share price data is changed in retrospect, thus leaving invalid data in the cache. In this case, you would need to delete the cache file, /tmp/cached-quote.dat, thereby removing the whole cash. Filling the file again will not take much effort because web requests to the financial servers efficiently retrieve high volumes of data. Enjoy watching your wealth grow!

The Author

Michael Schilli works as a Software Developer at Yahoo!, Sunnyvale, California. He wrote "Perl Power" for Addison-Wesley and can be contacted at mailto:mschilli@perlmeister.com. His homepage is at http://perlmeister.com.

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