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• Database warehouse design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to seek some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• Perform case-insensitive lookup on an Array in MongoDB?

  - by Hal

  So, I've decided to get my feet wet with MongoDB and love it so far. It seems very fast and flexible which is great. But, I'm still going through the initial learning curve and as such, I'm spending hours digging for info on the most basic things. I've search throughout the MongoDB online documentation and have spent hours Googling through pages without any mention of this. I know Mongo is still quite new (v1.x) so it explains why there isn't much information yet. I've even trying looking for books on Mongo without much luck. So yes, I've tried to RTFM with no luck, so, now I turn to you. I have an Array of various Hashtags nested in each document (ie: #apples, #oranges, #Apples, #APPLES) and I would like to perform a case-insensitive find() to access all the documents containing apples in any case. It seems that find does support some regex with /i, but I can't seem to get this working either. Anyway, I hope this is a quick answer for someone. Here's my existing call in PHP which is case sensitive: $cursor = $collection->find(array( "hashtags" => array("#".$keyword)))->sort(array('$natural' => -1))->limit(10); Help?

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• Perl OO frameworks and program design - Moose and Conway's inside-out objects (Class::Std)

  - by Emmel

  This is more of a use-case type of question... but also generic enough to be more broadly applicable: In short, I'm working on a module that's more or less a command-line wrapper; OO naturally. Without going into too many details (unless someone wants them), there isn't a crazy amount of complexity to the system, but it did feel natural to have three or four objects in this framework. Finally, it's an open source thing I'll put out there, rather than a module with a few developers in the same firm working on it. First I implemented the OO using Class::Std, because Perl Best Practices (Conway, 2005) made a good argument for why to use inside-out objects. Full control over what attributes get accessed and so on, proper encapsulation, etc. Also his design is surprisingly simple and clever. I liked it, but then noticed that no one really uses this; in fact it seems Conway himself doesn't really recommend this anymore? So I moved to everyone's favorite, Moose. It's easy to use, although way way overkill feature-wise for what I want to do. The big, major downside is: it's got a slew of module dependencies that force users of my module to download them all. A minor downside is it's got way more functionality than I really need. What are recommendations? Inconvenience fellow developers by forcing them to use a possibly-obsolete module, or force every user of the module to download Moose and all its dependencies? Is there a third option for a proper Perl OO framework that's popular but neither of these two?

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• Scaling Literate Programming?

  - by Tetha

  Greetings. I have been looking at Literate Programming a bit now, and I do like the idea behind it: you basically write a little paper about your code and write down as much of the design decisions, the code probably surrounding the module, the inner workins of the module, assumptions and conclusions resulting from the design decisions, potential extension, all this can be written down in a nice way using tex. Granted, the first point: it is documentation. It must be kept up-to-date, but that should not be that bad, because your change should have a justification and you can write that down. However, how does Literate Programming Scale to a larger degree? Overall, Literate Programming is still just text. Very human readable text, of course, but still text, and thus, it is hard to follow large systems. For example, I reworked large parts of my compiler to use and some magic to chain compile steps together, because some "x.register_follower(y); y.register_follower(z); y.register_follower(a);..." got really unwieldy, and changing that to x y z a made it a bit better, even though this is at its breaking point, too. So, how does Literate Programming scale to larger systems? Does anyone try to do that? My thought would be to use LP to specify components that communicate with each other using event streams and chain all of these together using a subset of graphviz. This would be a fairly natural extension to LP, as you can extract a documentation -- a dataflow diagram -- from the net and also generate code from it really well. What do you think of it? -- Tetha.

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• Detecting browser capabilities and selective events for mouse and touch

  - by skidding

  I started using touch events for a while now, but I just stumbled upon quite a problem. Until now, I checked if touch capabilities are supported, and applied selective events based on that. Like this: if(document.ontouchmove === undefined){ //apply mouse events }else{ //apply touch events } However, my scripts stopped working in Chrome5 (which is currently beta) on my computer. I researched it a bit, and as I expected, in Chrome5 (as opposed to older Chrome, Firefox, IE, etc.) document.ontouchmove is no longer undefined but null. At first I wanted to submit a bug report, but then I realized: There are devices that have both mouse and touch capabilities, so that might be natural, maybe Chrome now defines it because my OS might support both types of events. So the solutions seems easy: Apply BOTH event types. Right? Well the problem now take place on mobile. In order to be backward compatible and support scripts that only use mouse events, mobile browsers might try to fire them as well (on touch). So then with both mouse and touch events set, a certain handler might be called twice every time. What is the way to approach this? Is there a better way to check and apply selective events, or must I ignore the problems that might occur if browsers fire both touch and mouse events at times?

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• What are the primitive Forth operators?

  - by Barry Brown

  I'm interested in implementing a Forth system, just so I can get some experience building a simple VM and runtime. When starting in Forth, one typically learns about the stack and its operators (DROP, DUP, SWAP, etc.) first, so it's natural to think of these as being among the primitive operators. But they're not. Each of them can be broken down into operators that directly manipulate memory and the stack pointers. Later one learns about store (!) and fetch (@) which can be used to implement DUP, SWAP, and so forth (ha!). So what are the primitive operators? Which ones must be implemented directly in the runtime environment from which all others can be built? I'm not interested in high-performance; I want something that I (and others) can learn from. Operator optimization can come later. (Yes, I'm aware that I can start with a Turing machine and go from there. That's a bit extreme.) Edit: What I'm aiming for is akin to bootstrapping an operating system or a new compiler. What do I need do implement, at minimum, so that I can construct the rest of the system out of those primitive building blocks? I won't implement this on bare hardware; as an educational exercise, I'd write my own minimal VM.

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• Database warehoue design: fact tables and dimension tables

  - by morpheous

  I am building a poor man's data warehouse using a RDBMS. I have identified the key 'attributes' to be recorded as: sex (true/false) demographic classification (A, B, C etc) place of birth date of birth weight (recorded daily): The fact that is being recorded My requirements are to be able to run 'OLAP' queries that allow me to: 'slice and dice' 'drill up/down' the data and generally, be able to view the data from different perspectives After reading up on this topic area, the general consensus seems to be that this is best implemented using dimension tables rather than normalized tables. Assuming that this assertion is true (i.e. the solution is best implemented using fact and dimension tables), I would like to see some help in the design of these tables. 'Natural' (or obvious) dimensions are: Date dimension Geographical location Which have hierarchical attributes. However, I am struggling with how to model the following fields: sex (true/false) demographic classification (A, B, C etc) The reason I am struggling with these fields is that: They have no obvious hierarchical attributes which will aid aggregation (AFAIA) - which suggest they should be in a fact table They are mostly static or very rarely change - which suggests they should be in a dimension table. Maybe the heuristic I am using above is too crude? I will give some examples on the type of analysis I would like to carryout on the data warehouse - hopefully that will clarify things further. I would like to aggregate and analyze the data by sex and demographic classification - e.g. answer questions like: How does male and female weights compare across different demographic classifications? Which demographic classification (male AND female), show the most increase in weight this quarter. etc. Can anyone clarify whether sex and demographic classification are part of the fact table, or whether they are (as I suspect) dimension tables.? Also assuming they are dimension tables, could someone elaborate on the table structures (i.e. the fields)? The 'obvious' schema: CREATE TABLE sex_type (is_male int); CREATE TABLE demographic_category (id int, name varchar(4)); may not be the correct one.

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• Should programmers do Pro Bono work? where are the code public defenders?

  - by Tj Kellie

  How many projects are people doing based on the Bro Bono publico ideals versus working for the highest wage or potential for a cash-in-buy-out payday? For years lawyers have been called out for excessive gathering of wealth from high bill rates and huge settlement deals, hiring out their knowledge and skills to the highest bidders. People call for them to do more for free, use the laws and their time to defend or further some cause thats in the public's best interest. Is professional software development that different? So many bright people and so much knowledge of complex systems. Do you think that there is enough of a "Pro Bono" movement to solve the social and public problems in the industry right now? If so what are the examples to point to? OLPC? NOTE: Saying that open source software is the same as pro bono misses the point completely. I was looking for specific projects with a social context, not just group-sourcing for free software. Just because your not making anyone pay for your software does not mean its doing anyone any good. I'm not calling out manual enforcement of pro bono work for programmers, really just want some objective opinions and concrete examples of social-minded software/tech development projects like the One Laptop Per Child project. I'm sure open source would be a natural tie-in for some.

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• Autodetect Presence of CSV Headers in a File

  - by banzaimonkey

  Short question: How do I automatically detect whether a CSV file has headers in the first row? Details: I've written a small CSV parsing engine that places the data into an object that I can access as (approximately) an in-memory database. The original code was written to parse third-party CSV with a predictable format, but I'd like to be able to use this code more generally. I'm trying to figure out a reliable way to automatically detect the presence of CSV headers, so the script can decide whether to use the first row of the CSV file as keys / column names or start parsing data immediately. Since all I need is a boolean test, I could easily specify an argument after inspecting the CSV file myself, but I'd rather not have to (go go automation). I imagine I'd have to parse the first 3 to ? rows of the CSV file and look for a pattern of some sort to compare against the headers. I'm having nightmares of three particularly bad cases in which: The headers include numeric data for some reason The first few rows (or large portions of the CSV) are null There headers and data look too similar to tell them apart If I can get a "best guess" and have the parser fail with an error or spit out a warning if it can't decide, that's OK. If this is something that's going to be tremendously expensive in terms of time or computation (and take more time than it's supposed to save me) I'll happily scrap the idea and go back to working on "important things". I'm working with PHP, but this strikes me as more of an algorithmic / computational question than something that's implementation-specific. If there's a simple algorithm I can use, great. If you can point me to some relevant theory / discussion, that'd be great, too. If there's a giant library that does natural language processing or 300 different kinds of parsing, I'm not interested.

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• Academic question: typename

  - by Arman

  Hi, recently I accounted with a "simple problem" of porting code from VC++ to gcc/intel. The code is compiles w/o error on VC++: #include <vector> using std::vector; template <class T> void test_vec( std::vector<T> &vec) { typedef std::vector<T> M; /*==> add here typename*/ M::iterator ib=vec.begin(),ie=vec.end(); }; int main() { vector<double> x(100, 10); test_vec<double>(x); return 0; } then with g++ we have some unclear errors: g++ t.cpp t.cpp: In function 'void test_vec(std::vector<T, std::allocator<_CharT> >&)': t.cpp:13: error: expected `;' before 'ie' t.cpp: In function 'void test_vec(std::vector<T, std::allocator<_CharT> >&) [with T = double]': t.cpp:18: instantiated from here t.cpp:12: error: dependent-name 'std::M::iterator' is parsed as a non-type, but instantiation yields a type t.cpp:12: note: say 'typename std::M::iterator' if a type is meant If we add typename before iterator the code will compile w/o pb. If it is possible to make a compiler which can understand the code written in the more "natural way", then for me is unclear why we should add typename? Which rules of "C++ standards"(if there are some) will be broken if we allow all compilers to use without "typename"? kind regards Arman.

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• haskell: a data structure for storing ascending integers with a very fast lookup

  - by valya

  Hello! (This question is related to my previous question, or rather to my answer to it.) I want to store all qubes of natural numbers in a structure and look up specific integers to see if they are perfect cubes. For example, cubes = map (\x -> x*x*x) [1..] is_cube n = n == (head $ dropWhile (<n) cubes) It is much faster than calculating the cube root, but It has complexity of O(n^(1/3)) (am I right?). I think, using a more complex data structure would be better. For example, in C I could store a length of an already generated array (not list - for faster indexing) and do a binary search. It would be O(log n) with lower ?oefficient than in another answer to that question. The problem is, I can't express it in Haskell (and I don't think I should). Or I can use a hash function (like mod). But I think it would be much more memory consuming to have several lists (or a list of lists), and it won't lower the complexity of lookup (still O(n^(1/3))), only a coefficient. I thought about a kind of a tree, but without any clever ideas (sadly I've never studied CS). I think, the fact that all integers are ascending will make my tree ill-balanced for lookups. And I'm pretty sure this fact about ascending integers can be a great advantage for lookups, but I don't know how to use it properly (see my first solution which I can't express in Haskell).

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• Bash Templating: How to build configuration files from templates with Bash?

  - by FractalizeR

  Hello. I'm writting a script to automate creating configuration files for Apache and PHP for my own webserver. I don't want to use any GUIs like CPanel or ISPConfig. I have some templates of Apache and PHP configuration files. Bash script needs to read templates, make variable substitution and output parsed templates into some folder. What is the best way to do that? I can think of several ways. Which one is the best or may be there are some better ways to do that? I want to do that in pure Bash (it's easy in PHP for example) 1)http://stackoverflow.com/questions/415677/how-to-repace-variables-in-a-nix-text-file template.txt: the number is ${i} the word is ${word} script.sh: #!/bin/sh #set variables i=1 word="dog" #read in template one line at the time, and replace variables #(more natural (and efficient) way, thanks to Jonathan Leffler) while read line do eval echo "$line" done < "./template.txt" BTW, how do I redirect output to external file here? Do I need to escape something if variables contain, say, quotes? 2) Using cat & sed for replacing each variable with it's value: Given template.txt: The number is ${i} The word is ${word} Command: cat template.txt | sed -e "s/\${i}/1/" | sed -e "s/\${word}/dog/" Seems bad to me because of the need to escape many different symbols and with many variables the line will be tooooo long. Can you think of some other elegant and safe solution?

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• How do I find the most “Naturally" direct route using A-star (A*)

  - by Greg B

  I have implemented the A* algorithm in AS3 and it works great except for one thing. Often the resulting path does not take the most “natural” or smooth route to the target. In my environment the object can move diagonally as inexpensively as it can move horizontally or vertically. Here is a very simple example; the start point is marked by the S, and the end (or finish) point by the F. | | | | | | | | | | |S| | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | As you can see, during the 1st round of finding, nodes [0,2], [1,2], [2,2] will all be added to the list of possible node as they all have a score of N. The issue I’m having comes at the next point when I’m trying to decide which node to proceed with. In the example above I am using possibleNodes[0] to choose the next node. If I change this to possibleNodes[possibleNodes.length-1] I get the following path. | | | | | | | | | | |S| | | | | | | | | | |x| | | | | | | | | | |x| | | | | | | | | | |x| | | | | | | | |x| | | | | | | | |x| | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | And then with possibleNextNodes[Math.round(possibleNextNodes.length / 2)-1] | | | | | | | | | | |S| | | | | | | | | |x| | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | x| | | | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | All these paths have the same cost as they all contain the same number of steps but, in this situation, the most sensible path would be as follows... | | | | | | | | | | |S| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |x| | | | | | | | | |F| | | | | | | | | | | | | | | | | | | | | | | | | | | | | Is there a formally accepted method of making the path appear more sensible rather than just mathematically correct?

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• How to force c# binary int division to return a double?

  - by Wayne

  How to force double x = 3 / 2; to return 1.5 in x without the D suffix or casting? Is there any kind of operator overload that can be done? Or some compiler option? Amazingly, it's not so simple to add the casting or suffix for the following reason: Business users need to write and debug their own formulas. Presently C# is getting used like a DSL (domain specific language) in that these users aren't computer science engineers. So all they know is how to edit and create a few types of classes to hold their "business rules" which are generally just math formulas. But they always assume that double x = 3 / 2; will return x = 1.5 however in C# that returns 1. A. they always forget this, waste time debugging, call me for support and we fix it. B. they think it's very ugly and hurts the readability of their business rules. As you know, DSL's need to be more like natural language. Yes. We are planning to move to Boo and build a DSL based on it but that's down the road. Is there a simple solution to make double x = 3 / 2; return 1.5 by something external to the class so it's invisible to the users? Thanks! Wayne

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• How to force c# binary int division to return a double?

  - by Wayne

  How to force double x = 3 / 2; to return 1.5 in x without the D suffix or casting? Is there any kind of operator overload that can be done? Or some compiler option? Amazingly, it's not so simple to add the casting or suffix for the following reason: Business users need to write and debug their own formulas. Presently C# is getting used like a DSL (domain specific language) in that these users aren't computer science engineers. So all they know is how to edit and create a few types of classes to hold their "business rules" which are generally just math formulas. But they always assume that double x = 3 / 2; will return x = 1.5 however in C# that returns 1. A. they always forget this, waste time debugging, call me for support and we fix it. B. they think it's very ugly and hurts the readability of their business rules. As you know, DSL's need to be more like natural language. Yes. We are planning to move to Boo and build a DSL based on it but that's down the road. Is there a simple solution to make double x = 3 / 2; return 1.5 by something external to the class so it's invisible to the users? Thanks! Wayne

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• Map large integer to a phrase

  - by Alexander Gladysh

  I have a large and "unique" integer (actually a SHA1 hash). I want (for no other reason than to have fun) to find an algorithm to convert that SHA1 hash to a (pseudo-)English phrase. The conversion should be reversible (i.e., knowing the algorithm, one must be able to convert the phrase back to SHA1 hash.) The possible usage of the generated phrase: the human readable version of Git commit ID, like a motto for a given program version (which is built from that commit). (As I said, this is "for fun". I don't claim that this is very practical — or be much more readable than the SHA1 itself.) A better algorithm would produce shorter, more natural-looking, more unique phrases. The phrase need not make sense. I would even settle for a whole paragraph of nonsense. (Though quality — englishness — of a paragraph should probably be better than for a mere phrase.) A variation: it is OK if I will be able to work only with a part of hash. Say, first six digits is OK. Possible approach: In the past I've attempted to build a probability table (of words), and generate phrases as Markov chains, seeding the generator (picking branches from probability tree), according to the bits I read from the SHA. This was not very successful, the resulting phrases were too long and ugly. I'm not sure if this was a bug, or the general flaw in the algorithm, since I had to abandon it early enough. Now I'm thinking about attempting to solve the problem once again. Any advice on how to approach this? Do you think Markov chain approach can work here? Something else?

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• Writing re-entrant lexer with Flex

  - by Viet

  I'm newbie to flex. I'm trying to write a simple re-entrant lexer/scanner with flex. The lexer definition goes below. I get stuck with compilation errors as shown below (yyg issue): reentrant.l: /* Definitions */ digit [0-9] letter [a-zA-Z] alphanum [a-zA-Z0-9] identifier [a-zA-Z_][a-zA-Z0-9_]+ integer [0-9]+ natural [0-9]*[1-9][0-9]* decimal ([0-9]+\.|\.[0-9]+|[0-9]+\.[0-9]+) %{ #include <stdio.h> #define ECHO fwrite(yytext, yyleng, 1, yyout) int totalNums = 0; %} %option reentrant %option prefix="simpleit_" %% ^(.*)\r?\n printf("%d\t%s", yylineno++, yytext); %% /* Routines */ int yywrap(yyscan_t yyscanner) { return 1; } int main(int argc, char* argv[]) { yyscan_t yyscanner; if(argc < 2) { printf("Usage: %s fileName\n", argv[0]); return -1; } yyin = fopen(argv[1], "rb"); yylex(yyscanner); return 0; } Compilation errors: vietlq@mylappie:~/Desktop/parsers/reentrant$ gcc lex.simpleit_.c reentrant.l: In function ‘main’: reentrant.l:44: error: ‘yyg’ undeclared (first use in this function) reentrant.l:44: error: (Each undeclared identifier is reported only once reentrant.l:44: error: for each function it appears in.)

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• Should I move big data blobs in JSON or in separate binary connection?

  - by Amagrammer

  QUESTION: Is it better to send large data blobs in JSON for simplicity, or send them as binary data over a separate connection? If the former, can you offer tips on how to optimize the JSON to minimize size? If the latter, is it worth it to logically connect the JSON data to the binary data using an identifier that appears in both, e.g., as "data" : "< unique identifier " in the JSON and with the first bytes of the data blob being < unique identifier ? CONTEXT: My iPhone application needs to receive JSON data over the 3G network. This means that I need to think seriously about efficiency of data transfer, as well as the load on the CPU. Most of the data transfers will be relatively small packets of text data for which JSON is a natural format and for which there is no point in worrying much about efficiency. However, some of the most critical transfers will be big blobs of binary data -- definitely at least 100 kilobytes of data, and possibly closer to 1 megabyte as customers accumulate a longer history with the product. (Note: I will be caching what I can on the iPhone itself, but the data still has to be transferred at least once.) It is NOT streaming data. I will probably use a third-party JSON SDK -- the one I am using during development is here. Thanks

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• SQLAlchemy DetachedInstanceError with regular attribute (not a relation)

  - by haridsv

  I just started using SQLAlchemy and get a DetachedInstanceError and can't find much information on this anywhere. I am using the instance outside a session, so it is natural that SQLAlchemy is unable to load any relations if they are not already loaded, however, the attribute I am accessing is not a relation, in fact this object has no relations at all. I found solutions such as eager loading, but I can't apply to this because this is not a relation. I even tried "touching" this attribute before closing the session, but it still doesn't prevent the exception. What could be causing this exception for a non-relational property even after it has been successfully accessed once before? Any help in debugging this issue is appreciated. I will meanwhile try to get a reproducible stand-alone scenario and update here. Update: This is the actual exception message with a few stacks: File "/home/hari/bin/lib/python2.6/site-packages/SQLAlchemy-0.6.1-py2.6.egg/sqlalchemy/orm/attributes.py", line 159, in __get__ return self.impl.get(instance_state(instance), instance_dict(instance)) File "/home/hari/bin/lib/python2.6/site-packages/SQLAlchemy-0.6.1-py2.6.egg/sqlalchemy/orm/attributes.py", line 377, in get value = callable_(passive=passive) File "/home/hari/bin/lib/python2.6/site-packages/SQLAlchemy-0.6.1-py2.6.egg/sqlalchemy/orm/state.py", line 280, in __call__ self.manager.deferred_scalar_loader(self, toload) File "/home/hari/bin/lib/python2.6/site-packages/SQLAlchemy-0.6.1-py2.6.egg/sqlalchemy/orm/mapper.py", line 2323, in _load_scalar_attributes (state_str(state))) DetachedInstanceError: Instance <ReportingJob at 0xa41cd8c> is not bound to a Session; attribute refresh operation cannot proceed The partial model looks like this: metadata = MetaData() ModelBase = declarative_base(metadata=metadata) class ReportingJob(ModelBase): __tablename__ = 'reporting_job' job_id = Column(BigInteger, Sequence('job_id_sequence'), primary_key=True) client_id = Column(BigInteger, nullable=True) And the field client_id is what is causing this exception with a usage like the below: Query: jobs = session \ .query(ReportingJob) \ .filter(ReportingJob.job_id == job_id) \ .all() if jobs: # FIXME(Hari): Workaround for the attribute getting lazy-loaded. jobs[0].client_id return jobs[0] This is what triggers the exception later out of the session scope: msg = msg + ", client_id: %s" % job.client_id

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• When *not* to use prepared statements?

  - by Ben Blank

  I'm re-engineering a PHP-driven web site which uses a minimal database. The original version used "pseudo-prepared-statements" (PHP functions which did quoting and parameter replacement) to prevent injection attacks and to separate database logic from page logic. It seemed natural to replace these ad-hoc functions with an object which uses PDO and real prepared statements, but after doing my reading on them, I'm not so sure. PDO still seems like a great idea, but one of the primary selling points of prepared statements is being able to reuse them… which I never will. Here's my setup: The statements are all trivially simple. Most are in the form SELECT foo,bar FROM baz WHERE quux = ? ORDER BY bar LIMIT 1. The most complex statement in the lot is simply three such selects joined together with UNION ALLs. Each page hit executes at most one statement and executes it only once. I'm in a hosted environment and therefore leery of slamming their servers by doing any "stress tests" personally. Given that using prepared statements will, at minimum, double the number of database round-trips I'm making, am I better off avoiding them? Can I use PDO::MYSQL_ATTR_DIRECT_QUERY to avoid the overhead of multiple database trips while retaining the benefit of parametrization and injection defense? Or do the binary calls used by the prepared statement API perform well enough compared to executing non-prepared queries that I shouldn't worry about it? EDIT: Thanks for all the good advice, folks. This is one where I wish I could mark more than one answer as "accepted" — lots of different perspectives. Ultimately, though, I have to give rick his due… without his answer I would have blissfully gone off and done the completely Wrong Thing even after following everyone's advice. :-) Emulated prepared statements it is!

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• Managing resource closure in a servlet container

  - by Steven Schlansker

  I'm using Tomcat as a servlet container, and have many WARs deployed. Many of the WARs share common base classes, which are replicated in each context due to the different classloaders, etc. How can I ensure resource cleanup on context destruction, without hooking each and every web.xml file to add context listeners? Ideally, I'd like something along the lines of class MyResourceHolder implements SomeListenerInterface { private SomeResource resource; { SomeContextThingie.registerDestructionListener(this); } public void onDestroy() { resource.close(); } } I could put something in each web.xml, but since there are potentially many WARs and only ones that actually initialize the resource need to clean it up, it seems more natural to register for cleanup when the resource is initialized rather than duplicating a lot of XML configuration and then maybe cleaning up. (In this particular case, I'm initiating an orderly shutdown of a SQL connection pool. But I see this being useful in many other situations as well...) I'm sure there's some blisteringly obvious solution out there, but my Google-fu is failing me right now. Thanks!

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• Exponential regression : p-value and F significance

  - by Saravanan K

  I am new to statistics. I have a set of independent data and dependent data (X,Y), where I would like to do an exponential regression to obtain its p-value and significant F (already obtained R2 and also the coefficients through mathematical calculation). What is the natural evolution from the (X,Y) data to mathematically calculate those variables. Spent a week on the internet to study this but unable to find the right answer. Often an exponential data, y=be^(mx) will be converted first to a linear data, ln y = mx + ln b . Then a linear regression will done on the converted data, obtaining its p-value etc. Assume we use a statistical tool such as Excel's Analysis ToolPak: Data Analysis : Regression, it will produce a result such as below, I believe the p-value and Significant F value is representing the converted linear data and not the original exponential data. Questions: What is the approach/steps used by Excel to get the p-value and Significant F value for the converted linear data as shown in the statistic output in the image above? It is not clear in their help page or website. Can the p-value and Significant F could be mathematically calculated for exponential regression without using a statistical tool? Can you assist to point me to the right link if this has been answered before.

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• What framework would allow for the largest coverage of freelance developers in the media/digital mar

  - by optician

  This question is not about which is the best, it is about which makes the most business sense to use as a company's platform of choice for ongoing freelance development. I'm currently trying to decide what framework to move my company in regarding frameworks for web application work. Options are ASP.NET MVC Django CakePHP/Symfony etc.. Struts Pearl on Rails Please feel free to add more to the discussion. I currently work in ASP.NET MVC in my Spare time, and find it incredibly enjoyable to work with. It is my first experince with an MVC framework for the web, so I can't talk on the others. The reason for not pushing this at the company is that I feel that there are not many developers in the Media/Marketing world who would work with this, so it may be hard to extend the team, or at least cost more. I would like to move into learning and pushing Django, partly to learn python, partly to feel a bit cooler (all my geeky friends use Java/Python/c++). Microsoft is the dark side to most company's I work with (Marketing/Media focused). But again I'm worried about developers in this sector. PHP seems like the natural choice, but I'm scared by the sheer amount of possible frameworks, and also that the quality of developer may be lower. I know there are great php developers out there, but how many of them know multiple frameworks? Are they similar enough that anyone decent at php can pick them up? Just put struts in the list as an option, but personally I live with a Java developer, and considering my experience with c#, I'm just not that interested in learning Java (selfish personal geeky reasons) Final option was a joke http://www.bbc.co.uk/blogs/radiolabs/2007/11/perl_on_rails.shtml

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• Triangle numbers problem....show within 4 seconds

  - by Daredevil

  The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be: 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ... Let us list the factors of the first seven triangle numbers: 1: 1 3: 1,3 6: 1,2,3,6 10: 1,2,5,10 15: 1,3,5,15 21: 1,3,7,21 28: 1,2,4,7,14,28 We can see that 28 is the first triangle number to have over five divisors. Given an integer n, display the first triangle number having at least n divisors. Sample Input: 5 Output 28 Input Constraints: 1<=n<=320 I was obviously able to do this question, but I used a naive algorithm: Get n. Find triangle numbers and check their number of factors using the mod operator. But the challenge was to show the output within 4 seconds of input. On high inputs like 190 and above it took almost 15-16 seconds. Then I tried to put the triangle numbers and their number of factors in a 2d array first and then get the input from the user and search the array. But somehow I couldn't do it: I got a lot of processor faults. Please try doing it with this method and paste the code. Or if there are any better ways, please tell me.

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• Convert rank-per-candidate format to OpenSTV BLT format

  - by kibibu

  I recently gathered, using a questionnaire, a set of opinions on the importance of various software components. Figuring that some form of Condorcet voting method would be the best way to obtain an overall rank, I opted to use OpenSTV to analyze it. My data is in tabular format, space delimited, and looks more or less like: A B C D E F G # Candidates 5 2 4 3 7 6 1 # First ballot. G is ranked first, and E is ranked 7th 4 2 6 5 1 7 3 # Second ballot etc In this format, the number indicates the rank and the sequence order indicates the candidate. Each "candidate" has a rank (required) from 1 to 7, where a 1 means most important and a 7 means least important. No duplicates are allowed. This format struck me as the most natural way to represent the output, being a direct representation of the ballot format. The OpenSTV/BLT format uses a different method of representing the same info, conceptually as follows: G B D C A F E # Again, G is ranked first and E is ranked 7th E B G A D C F # etc The actual numeric file format uses the (1-based) index of the candidate, rather than the label, and so is more like: 7 2 4 3 1 6 5 # Same ballots as before. 5 2 7 1 4 3 6 # A -> 1, G -> 7 In this format, the number indicates the candidate, and the sequence order indicates the rank. The actual, real, BLT format also includes a leading weight and a following zero to indicate the end of each ballot, which I don't care too much about for this. My question is, what is the most elegant way to convert from the first format to the (numeric) second?

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