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Re: Lists and Loops

  • To: mathgroup at smc.vnet.net
  • Subject: [mg113025] Re: Lists and Loops
  • From: Albert Retey <awnl at gmx-topmail.de>
  • Date: Mon, 11 Oct 2010 05:17:45 -0400 (EDT)
  • References: <i8s5e7$935$1@smc.vnet.net>

Am 10.10.2010 12:44, schrieb Michaell Taylor:
> I am new to Mathematica and am probably too stuck in other languages, but
> but having a hard time with a simple listing building looping structure.
>  The code below is supposed to cycle through a list of stock tickers.  For
> each ticker it builds a list of certain financial data elements and adds
> each element to a list.  When the list is complete (all financial elements
> obtained), the list is written to a Mysql database.  The internal looping
> structure seems to work fine.  That is, if I execute the internal loop for a
> single ticker, the results are added to the database as planned.
> 
> However, the outer structure causes a problem in that the list continues to
> grow with each ticker.  The "mydata={}" line was meant to "reset" the list,
> but doesn't seem to be performing as expected.
> 
>  tickers = {"VNO", "AMB"}
> 
> fprop = {"Average50Day", "Average200Day"}
> 
> Do[
>  mydata = {t}
>    Do[
>     mydata = Append[mydata, FinancialData[t, i]],
>     {i, fprop}]
>    Print[mydata]
>    SQLInsert[connt, "reit" , {"ticker", "first", "second"}, mydata]
>    {t, tickers}]
> 
> 
> My error, no doubt is obvious to some. Any guidance would be greatly
> appreciated.

I think you are just missing some ; and , at the right places, I have
not tested it but this might work:

Do[
 mydata = {t};
 Do[mydata = Append[mydata, FinancialData[t, i]], {i, fprop}];
 Print[mydata];
 SQLInsert[connt, "reit", {"ticker", "first", "second"}, mydata],
 {t,tickers}
]

Using Do loops and Append is often neither elegant nor efficient in
Mathematica, something like this would probably be more Mathematica-ish:

mydata = Map[
   Function[{t}, Flatten[{t, FinancialData[t, #] & /@ fprop}]],
   tickers
   ];
SQLInsert[connt, "reit", {"ticker", "first", "second"}, mydata]

Depending on what you try to achieve it also might be more efficient to
insert all your data in one go as I did than to use a single SQLInsert
for each ticker.

hth,

albert



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