Re: read and write stock prices to file using arrays

On Fri, Apr 9, 2010 at 3:57 PM, Peter Miller <[e-mail]> wrote:
>> An idea would be to fill a hash with the data retrieved for each symbol:
>>
>> ticker_data =3D {}
>>
>> YahooFinance.get_quotes( quote_type, quote_symbols ) do |qt|
>> =A0 puts "QUOTING: #{qt.symbol}"
>> =A0 puts "#{qt.name}"
>> =A0 puts "#{qt.lastTrade}"
>> =A0 ticker_data[qt.symbol] =3D [qt.name, qt.lastTrade]
>> end
>
> I didn't realize a hash could point to more than one object. Awesome.

As Martin explained, it's just one object. It happens to be an array
with many other objects inside, or it could be a struct, for example:

Quote =3D Struct.new(:symbol, :name, :last_trade)
YahooFinance.get_quotes( quote_type, quote_symbols ) do |qt|
   ticker_data[qt.symbol] =3D Quote.new qt.symbol, qt.name, qt.last_trade
end

or another hash:

YahooFinance.get_quotes( quote_type, quote_symbols ) do |qt|
   ticker_data[qt.symbol] =3D {:symbol =3D> qt.symbol, :name =3D> qt.name,
:last_trade =3D> qt.last_trade}
end

depends on how you want to use it later.

>
>> and then write to the file the data in ticker_data. I can see
>> additional complexity if you want to keep the file exactly as it is
>> (with the comments) but inserting the retrieved data in place. The
>> easiest would be to just write ticker_data:
>
> this is why i was trying to do $ticker[lines] =3D line when storing the
> data. I thought I could point the index of the ticker symbol, which
> would tell me what line it was on, to my array $ticker. Then i wanted to
> use that index to write back the ticker data to the same line it came
> from.

The problem is that you can't really insert things "in the middle" of a fil=
e.
If you write something in the current position of a file (the cursor),
it will overwrite what's after, it doesn't push the rest of the file
to make space for what you are writing.

So, the usual simple way is to read the file, modify it in memory and
write it all again. If you want to preserve everything, you could
split the file in chunks with the comments, and replace the other
lines with the result of your calculation. For that, you will have to
keep track of which lines represent ticker data. For example
(untested):

TickerData =3D Struct.new :symbol, :file_position, :name, :last_trade

lines =3D File.readlines(filename)
tickers =3D {}
lines.each_with_index do |line, i|
 next if line =3D~ /^#/         # skip comments
 next if line.chomp.empty?    # skip empty lines
 symbol =3D line[/\w+/]
 tickers[symbol] =3D TickerData.new symbol, i #store the symbol and the
file position
end

YahooFinance.get_quotes( quote_type, tickers.keys ) do |qt|
   next unless tickers[qt.symbol]
   tickers[qt.symbol].name =3D qt.name
   tickers[qt.symbol].last_trade =3D qt.last_trade
end

Now you have the original lines in an array and a hash with all the
data, including to which line it corresponds, you can sub the line
with what you want, and then write the file back:

tickers.each do |symbol, ticker|
  lines[ticker.file_position] =3D "#{ticker.symbol} #{ticker.name}
#{ticker.last_trade}\n"
end

File.open(filename, "w") {|file| file.puts lines.join}

I think this should work but I haven't tested it.

Jesus.