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• cakePHP: Filter selected list by variable

  - by gonzela2006

  I'm on cakePHP 2. I have a problem and I need your help. Here is some code of my controller(StudentsController.php) specifically "edit" function: $students = $this -> Student -> find('list', array( 'order' => 'Student.name ASC' )); $this -> set('students', $students); How can I filter the list by the current student's class?? so the list will contain all students that has the same student's class I need some code like this $students = $this -> Student -> find('list', array( 'conditions' => array('Student.class_id' => CURRENT-STUDENT'S-CLASS), 'order' => 'Student.name ASC' )); $this -> set('students', $students); Please Advise Thanks, gonzela2006

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• Approximate timings for various operations on a "typical desktop PC" anno 2010

  - by knorv

  In the article "Teach Yourself Programming in Ten Years" Peter Norvig (Director of Research, Google) gives the following approximate timings for various operations on a typical 1GHz PC back in 2001: execute single instruction = 1 nanosec = (1/1,000,000,000) sec fetch word from L1 cache memory = 2 nanosec fetch word from main memory = 10 nanosec fetch word from consecutive disk location = 200 nanosec fetch word from new disk location (seek) = 8,000,000 nanosec = 8 millisec What would the corresponding timings be for your definition of a typical PC desktop anno 2010?

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• What is the best way to implement this composite GetHashCode()

  - by Frank Krueger

  I have a simple class: public class TileName { int Zoom, X, Y; public override bool Equals (object obj) { var o = obj as TileName; return (o != null) && (o.Zoom == Zoom) && (o.X == X) && (o.Y == Y); } public override int GetHashCode () { return (Zoom + X + Y).GetHashCode(); } } I was curious if I would get a better distribution of hash codes if I instead did something like: public override int GetHashCode () { return Zoom.GetHashCode() + X.GetHashCode() + Y.GetHashCode(); } This class is going to be used as a Dictionary key, so I do want to make sure there is a decent distribution.

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• What is the function from which all other functions can be derived?

  - by ChrisD

  I seem to remember reading about a function that could be used to make all other functions. Does anyone know what it is? And how could such a function be used? I can't remember where I read it and my google-fu is not strong enough.

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• O(log N) == O(1) - Why not?

  - by phoku

  Whenever I consider algorithms/data structures I tend to replace the log(N) parts by constants. Oh, I know log(N) diverges - but does it matter in real world applications? log(infinity) < 100 for all practical purposes. I am really curious for real world examples where this doesn't hold. To clarify: I understand O(f(N)) I am curious about real world examples where the asymptotic behaviour matters more than the constants of the actual performance. If log(N) can be replaced by a constant it still can be replaced by a constant in O( N log N). This question is for the sake of (a) entertainment and (b) to gather arguments to use if I run (again) into a controversy about the performance of a design.

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• maximum memory which malloc can allocate!

  - by Vikas

  I was trying to figure out how much memory I can malloc to maximum extent on my machine (1 Gb RAM 160 Gb HD Windows platform). I read that maximum memory malloc can allocate is limited to physical memory.(on heap) Also when a program exceeds consumption of memory to a certain level, the computer stops working because other applications do not get enough memory that they require. So to confirm,I wrote a small program in C, int main(){ int *p; while(1){ p=(int *)malloc(4); if(!p)break; } } Hoping that there would be a time when memory allocation will fail and loop will be breaked. But my computer hanged as It was an infinite loop. I waited for about an hour and finally I had to forcely shut down my computer. Some questions: Does malloc allocate memory from HD also? What was the reason for above behaviour? Why didn't loop breaked at any point of time.? Why wasn't there any allocation failure?

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• how to merge file lines having the same first word in python?

  - by user1377135

  I have written a program to merge lines in a file containing the same first word in python. However I am unable to get the desired output. Can anyone please suggest me the mistake in my program? input "file.txt" line1: a b c line2: a b1 c1 line3: d e f line4: i j k line5: i s t line6: i m n ` output a b c a b1 c1 d e f i j k i s t i m n my code a = [line.split() for line in open('file.txt')] L=[] for i in range(0,len(a)): j=i while True: if a[j][0] == a[j+1][0]: L.append(a[j]) L.append(a[j+1]) j=j+2 else: print a[i] print L break

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• UV-vis detector [Hardware]

  - by aaa

  hello. This is not hundred percent programming related question, but I was not able to find answer on the net. Is there some kind of detector to record frequency/intensity of light radiation source? something like spectroscopy detector, but instead of actual machine, just the module which can be integrated in project. I have tried searching on Google but I do not even know what such device is called if you know the more appropriate place to ask, can you let me know please. Thank you

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• Three most critical programming concepts

  - by Todd

  I know this has probably been asked in one form or fashion but I wanted to pose it once again within the context of my situation (and probably others here @ SO). I made a career change to Software Engineering some time ago without having an undergrad or grad degree in CS. I've supplemented my undergrad and grad studies in business with programming courses (VB, Java,C, C#) but never performed academic coursework in the other related disciplines (algorithms, design patterns, discrete math, etc.)...just mostly self-study. I know there are several of you who have either performed interviews and/or made hiring decisions. Given recent trends in demand, what would you say are the three most essential Comp Sci concepts that a developer should have a solid grasp of outside of language syntax? For example, I've seen blog posts of the "Absolute minimum X that every programmer must know" variety...that's what I'm looking for. Again if it's truly a redundancy please feel free to close; my feelings won't be hurt. (Closest ones I could find were http://stackoverflow.com/questions/164048/basic-programming-algorithmic-concepts- which was geared towards a true beginner, and http://stackoverflow.com/questions/648595/essential-areas-of-knowledge-which I didn't feel was concrete enough). Thanks in advance all! T.

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• Standard term for a thread I/O reorder buffer?

  - by Crashworks

  I have a case where many threads all concurrently generate data that is ultimately written to one long, serial file. I need to somehow serialize these writes so that the file gets written in the right order. ie, I have an input queue of 2048 jobs j0..jn, each of which produces a chunk of data oi. The jobs run in parallel on, say, eight threads, but the output blocks have to appear in the file in the same order as the corresponding input blocks — the output file has to be in the order o0o1o2... The solution to this is pretty self evident: I need some kind of buffer that accumulates and writes the output blocks in the correct order, similar to a CPU reorder buffer in Tomasulo's algorithm, or to the way that TCP reassembles out-of-order packets before passing them to the application layer. Before I go code it, I'd like to do a quick literature search to see if there are any papers that have solved this problem in a particularly clever or efficient way, since I have severe realtime and memory constraints. I can't seem to find any papers describing this though; a Scholar search on every permutation of [threads, concurrent, reorder buffer, reassembly, io, serialize] hasn't yielded anything useful. I feel like I must just not be searching the right terms. Is there a common academic name or keyword for this kind of pattern that I can search on?

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• Convert a post-order binary tree traversal index to an level-order (breadth-first) index

  - by strfry

  Assuming a complete binary tree, each node can be adressed with the position it appears in a given tree traversal algorithm. For example, the node indices of a simple complete tree with height 3 would look like this: breadth first (aka level-order): 0 / \ 1 2 / \ / \ 3 4 5 6 post-order dept first: 6 / \ 2 5 / \ / \ 0 1 3 4 The height of the tree and an index in the post-order traversal is given. How can i calculate the breadth first index from this information?

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• CS Majors: Hardest concept(s) you learned in school?

  - by Mark Lubin

  For the CS majors out there what were the hardest CS classes or concepts that you learned in your undergraduate schooling? Did you find once you learned the basics,(data structs, OOP fundamentals, discrete math, pointers, recursion, etc) the rest followed naturally or did you hit a wall at any point in your higher classes like OS'es and Compilers? Thanks for the input!

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• why IEEE floating point number calculate exponent using a biased form?

  - by lenatis

  let's say, for the float type in c, according to the IEEE floating point specification, there are 8-bit used for the fraction filed, and it is calculated as first taken these 8-bit and translated it into an unsigned number, and then minus the BIASE, which is 2^7 - 1 = 127, and the result is an exponent ranges from -127 to 128, inclusive. But why can't we just treat these 8-bit pattern as a signed number, since the resulting range is [-128,127], which is almost the same as the previous one.

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• P implies Q, how to read in english

  - by user177883

  how to read P implies Q in classical logic? example : Distributivity: Ka(X->Y) -> (KaX -> KaY) This is model logic which uses classical logic rules. KaX : a knows the that X is true. I m curious about how to read implication in english? if then else?

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• Can a variable like 'int' be considered a primitive/fundamental data structure?

  - by Ravi Gupta

  A rough definition of a data structure is that it allows you to store data and apply a set of operations on that data while preserving consistency of data before and after the operation. However some people insist that a primitive variable like 'int' can also be considered as a data structure. I get that part where it allows you to store data but I guess the operation part is missing. Primitive variables don't have operations attached to them. So I feel that unless you have a set of operations defined and attached to it you cannot call it a data structure. 'int' doesn't have any operation attached to it, it can be operated upon with a set of generic operators. Please advise if I got something wrong here.

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• A Computer Poem for those over 30 [closed]

  - by arvind

  I recd. a very good poem, that i wished to share with everyone. so for once we need no answers. lol ;-) A computer was something on TV From a science fiction show of note A window was something you hated to clean And ram was the cousin of a goat. Meg was the name of my girlfriend And gig was a job for the nights Now they all mean different things And that really mega bytes. An application was for employment A program was a TV show A cursor used profanity A keyboard was a piano.

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• How to keep a Generic list unmodified when its copy is modified?

  - by user1801934

  When I create a copy of the original list lstStudent in lstCopy and send the lstCopy to modification function, the lstStudent also gets modified. I want to keep this list unmodified. List<Student> lstStudent = new List<Student>(); Student s = new Student(); s.Name = "Akash"; s.ID = "1"; lstStudent.Add(s); List<Student> lstCopy = new List<Student>(lstStudent); Logic.ModifyList(lstCopy); // "Want to use lstStudent(original list) for rest part of the code" public static void ModifyList(List<Student> lstIntegers) { foreach (Student s in lstIntegers) { if (s.ID.Equals("1")) { s.ID = "4"; s.Name = "APS"; } } }

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• Count the number of objects in an Image

  - by kunjaan

  I am investigating the possibility of image processing to identify certain objects and also count them in an image. I will be given a picture and I need to identify the number of boxes present in that image. Does anybody have any experience with any Machine Vision/ Image Processing libraries like ImageJ, Fiji, JAI, jMagick ,Java Vision Toolkit? Which do you think is best suited for the job? What do you guys suggest? If the APIs can be used from Java, it would be better. Thank you. Edit: I am dealing with warehouse brown boxes. Yes I am talking about regular photos. The source is usually a mobile phone picture.

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• whats the term used to describe sending the same message to a system and reciving the same response

  - by Bluephlame

  I"m looking for a term here. in messaging systems you send a request, and it processes and sends a response. if that same request is sent it should return the same response, (but not necessarily process the details) This would be like submitting financial details twice.

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• What's the term for a program or system that is used to maintain itself?

  - by eft

  And I don't mean skynet. I'm thinking of say a compiler application that is used to compile itself, a VCS that tracks its own source code etc.

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• Is the integer-factorization problem (used for many cryptographic applications) NP-Complete?

  - by Gail

  As the question states, does the integer-factorization problem fall into the class of NP-Complete problems?

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• Is the language A = {0^n 1^n 0^n} context free?

  - by Tony

  Hi, I was just putting some thought into different languages (as I'm reviewing for final exams coming up) and I can not think of a valid pushdown automata to handle the language A = {0^n 1^n 0^n | n = 0}. This is not a context-free language, am I correct?

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• How can I achieve this kind of relationship (inheritance, composition, something else)?

  - by Tim

  I would like to set up a foundation of classes for an application, two of which are person and student. A person may or may not be a student and a student is always a person. The fact that a student “is a” person led me to try inheritance, but I can't see how to make it work in the case where I have a DAO that returns an instance of person and I then want to determine if that person is a student and call student related methods for it. class Person { private $_firstName; public function isStudent() { // figure out if this person is a student return true; // (or false) } } class Student extends Person { private $_gpa; public function getGpa() { // do something to retrieve this student's gpa return 4.0; // (or whatever it is) } } class SomeDaoThatReturnsPersonInstances { public function find() { return new Person(); } } $myPerson = SomeDaoThatReturnsPersonInstances::find(); if($myPerson->isStudent()) { echo 'My person\'s GPA is: ', $myPerson->getGpa(); } This obviously doesn't work, but what is the best way to achieve this effect? Composition doesn't sond right in my mind because a person does not “have a” student. I'm not looking for a solution necessarily but maybe just a term or phrase to search for. Since I'm not really sure what to call what I'm trying to do, I haven't had much luck. Thank you!

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• Why call-by-value evaluation strategy is not Turing complete?

  - by Roman

  I'm reading an article about different evaluation strategies (I linked article in wiki, but I'm reading another one not in English). And it says that unlike to call-by-name and call-by-need strategies, call-by-value strategy is not Turing complete. Can anybody explain, please, why is it so? If it's possible, add an example pls.

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• wrap all lines that are longer than line length

  - by user1919840

  I am writing a program that limits each line to a certain length. this is what i got so far, i am almost done but i still need to cut each line, but i cant figure it out. def main(): filename = input("Please enter the name of the file to be used: ") openFile = open(filename, 'r+') file = openFile.read() lLength = int(input("enter a number between 10 & 20: ")) while (lLength < 10) or (lLength > 20) : print("Invalid input, please try again...") lLength = int(input("enter a number between 10 & 20: ")) wr = textwrap.TextWrapper() wraped = wr.wrap(file) print("Here is your output formated to a max of", lLength, "characters per line: ") wr.width = lLength wr.expand_tabs = True for lines in wraped: print(lines) an example of what the output SHOULD be is this. If the file specified contains this text: hgytuinghdt #here the length is 11 ughtnjuiknshfyth #here the length is 16 nmjhkaiolgytuhngjuin #here the length is 20 and the lLength is specified to 15 then this should print out: hgytuinghdt ughtnjuiknshfyt h nmjhkaiolgytuhng juin Thanks.

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