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• Algorithm for assigning a unique series of bits for each user?

  - by Mark

  The problem seems simple at first: just assign an id and represent that in binary. The issue arises because the user is capable of changing as many 0 bits to a 1 bit. To clarify, the hash could go from 0011 to 0111 or 1111 but never 1010. Each bit has an equal chance of being changed and is independent of other changes. What would you have to store in order to go from hash - user assuming a low percentage of bit tampering by the user? I also assume failure in some cases so the correct solution should have an acceptable error rate. I would an estimate the maximum number of bits tampered with would be about 30% of the total set. I guess the acceptable error rate would depend on the number of hashes needed and the number of bits being set per hash. I'm worried with enough manipulation the id can not be reconstructed from the hash. The question I am asking I guess is what safe guards or unique positioning systems can I use to ensure this happens.

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• Error in connection in ruby.

  - by piemesons

  require 'rubygems' require 'mysql' db = Mysql.connect('localhost', 'root', '', 'mohit') //db.rb:4: undefined method `connect' for Mysql:Class (NoMethodError) //undefined method `real_connect' for Mysql:Class (NoMethodError) db.query("CREATE TABLE people ( id integer primary key, name varchar(50), age integer)") db.query("INSERT INTO people (name, age) VALUES('Chris', 25)") begin query = db.query('SELECT * FROM people') puts "There were #{query.num_rows} rows returned" query.each_hash do |h| puts h.inspect end rescue puts db.errno puts db.error end error i am geting is: undefined method `connect' for Mysql:Class (NoMethodError) OR undefined method `real_connect' for Mysql:Class (NoMethodError) EDIT return value of Mysql.methods ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "object_id", "__send__", "method_defined?", "instance_variable_defined?", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "instance_method", "hash", "autoload?", "dup", "to_enum", "instance_methods", "public_method_defined?", "instance_variables", "class_variable_defined?", "eql?", "constants", "id", "instance_eval", "singleton_methods", "module_exec", "const_missing", "taint", "instance_variable_get", "frozen?", "enum_for", "private_method_defined?", "public_instance_methods", "display", "instance_of?", "superclass", "method", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "public_class_method", "to_s", "<=", "const_set", "allocate", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "autoload", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"] return value of Mysql.methods(false) is []... blank array

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• Hibernate mapping Problem

  - by Geln Yang

  Hi, There is a table Item like, code,name 01,parent1 02,parent2 0101,child11 0102,child12 0201,child21 0202,child22 Create a java object and hbm xml to map the table.The Item.parent is a Item whose code is equal to the first two characters of its code : class Item{ String code; String name; Item parent; List<Item> children; .... setter/getter.... } <hibernate-mapping> <class name="Item" table="Item"> <id name="code" length="4" type="string"> <generator class="assigned" /> </id> <property name="name" column="name" length="50" not-null="true" /> <many-to-one name="parent" class="Item" not-found="ignore"> <formula> <![CDATA[ (select i.code,r.name from Item i where (case length(code) when 4 then i.code=SUBSTRING(code,1,2) else false end)) ]]> </formula> </many-to-one> <bag name="children"></bag> </class> </hibernate-mapping> I try to use formula to define the many-to-one relationship,but it doesn't work!Is there something wrong?Or is there other method? Thanks! ps,I use mysql database.

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• SFINAE + sizeof = detect if expression compiles

  - by FredOverflow

  I just found out how to check if operator<< is provided for a type. template<class T> T& lvalue_of_type(); template<class T> T rvalue_of_type(); template<class T> struct is_printable { template<class U> static char test(char(*)[sizeof( lvalue_of_type<std::ostream>() << rvalue_of_type<U>() )]); template<class U> static long test(...); enum { value = 1 == sizeof test<T>(0) }; typedef boost::integral_constant<bool, value> type; }; Is this trick well-known, or have I just won the metaprogramming Nobel prize? ;) EDIT: I made the code simpler to understand and easier to adapt with two global function template declarations lvalue_of_type and rvalue_of_type.

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• Non standard interaction among two tables to avoid very large merge

  - by riko

  Suppose I have two tables A and B. Table A has a multi-level index (a, b) and one column (ts). b determines univocally ts. A = pd.DataFrame( [('a', 'x', 4), ('a', 'y', 6), ('a', 'z', 5), ('b', 'x', 4), ('b', 'z', 5), ('c', 'y', 6)], columns=['a', 'b', 'ts']).set_index(['a', 'b']) AA = A.reset_index() Table B is another one-column (ts) table with non-unique index (a). The ts's are sorted "inside" each group, i.e., B.ix[x] is sorted for each x. Moreover, there is always a value in B.ix[x] that is greater than or equal to the values in A. B = pd.DataFrame( dict(a=list('aaaaabbcccccc'), ts=[1, 2, 4, 5, 7, 7, 8, 1, 2, 4, 5, 8, 9])).set_index('a') The semantics in this is that B contains observations of occurrences of an event of type indicated by the index. I would like to find from B the timestamp of the first occurrence of each event type after the timestamp specified in A for each value of b. In other words, I would like to get a table with the same shape of A, that instead of ts contains the "minimum value occurring after ts" as specified by table B. So, my goal would be: C: ('a', 'x') 4 ('a', 'y') 7 ('a', 'z') 5 ('b', 'x') 7 ('b', 'z') 7 ('c', 'y') 8 I have some working code, but is terribly slow. C = AA.apply(lambda row: ( row[0], row[1], B.ix[row[0]].irow(np.searchsorted(B.ts[row[0]], row[2]))), axis=1).set_index(['a', 'b']) Profiling shows the culprit is obviously B.ix[row[0]].irow(np.searchsorted(B.ts[row[0]], row[2]))). However, standard solutions using merge/join would take too much RAM in the long run. Consider that now I have 1000 a's, assume constant the average number of b's per a (probably 100-200), and consider that the number of observations per a is probably in the order of 300. In production I will have 1000 more a's. 1,000,000 x 200 x 300 = 60,000,000,000 rows may be a bit too much to keep in RAM, especially considering that the data I need is perfectly described by a C like the one I discussed above. How would I improve the performance?

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• java: retrieving the "canonical value" from a Set<T> where T has a custom equals()

  - by Jason S

  I have a class Foo which overrides equals() and hashCode() properly. I would like to also would like to use a HashSet<Foo> to keep track of "canonical values" e.g. I have a class that I would like to write like this, so that if I have two separate objects that are equivalent I can coalesce them into references to the same object: class Canonicalizer<T> { final private Set<T> values = new HashSet<T>(); public T findCanonicalValue(T value) { T canonical = this.values.get(value); if (canonical == null) { // not in the set, so put it there for the future this.values.add(value); return value; } else { return canonical; } } } except that Set doesn't have a "get" method that would return the actual value stored in the set, just the "contains" method that returns true or false. (I guess that it assumes that if you have an object that is equal to a separate object in the set, you don't need to retrieve the one in the set) Is there a convenient way to do this? The only other thing I can think of is to use a map and a list: class Canonicalizer<T> { // warning: neglects concurrency issues final private Map<T, Integer> valueIndex = new HashMap<T, Integer>(); final private List<T> values = new ArrayList<T>(); public T findCanonicalValue(T value) { Integer i = this.valueIndex.get(value); if (i == null) { // not in the set, so put it there for the future i = this.values.size(); this.values.add(value); this.valueIndex.put(value, i); return value; } else { // in the set return this.values.get(i); } } }

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• Are .NET's regular expressions Turing complete?

  - by Robert

  Regular expressions are often pointed to as the classical example of a language that is not Turning complete. For example "regular expressions" is given in as the answer to this SO question looking for languages that are not Turing complete. In my, perhaps somewhat basic, understanding of the notion of Turning completeness, this means that regular expressions cannot be used check for patterns that are "balanced". Balanced meaning have an equal number of opening characters as closing characters. This is because to do this would require you to have some kind of state, to allow you to match the opening and closing characters. However the .NET implementation of regular expressions introduces the notion of a balanced group. This construct is designed to let you backtrack and see if a previous group was matched. This means that a .NET regular expressions: ^(?<p>a)*(?<-p>b)*(?(p)(?!))$ Could match a pattern that: ab aabb aaabbb aaaabbbb ... etc. ... Does this means .NET's regular expressions are Turing complete? Or are there other things that are missing that would be required for the language to be Turing complete?

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• Linq2Sql: query - subquery optimisation

  - by Budda

  I have the following query: IList<InfrStadium> stadiums = (from sector in DbContext.sectors where sector.Type=typeValue select new InfrStadium(sector.TeamId) ).ToList(); and InfrStadium class constructor: private InfrStadium(int teamId) { IList<Sector> teamSectors = (from sector in DbContext.sectors where sector.TeamId==teamId select sector) .ToList<>(); ... work with data } Current implementation perform 1+n queries, where n - number of records fetched the 1st time. I want to optimize that. And another one I would love to do using 'group' operator in way like this: IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IEnumerable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } But attempt to launch query causes the following error: Expression of type 'System.Int32' cannot be used for constructor parameter of type 'System.Collections.Generic.IEnumerable`1[InfrStadiumSector]' Question 1: Could you please explain, what is wrong here, I don't understand why 'team_sectors' is applied as 'System.Int32'? I've tried to change query a little (replace IEnumerable with IQueryeable): IList<InfrStadium> stadiums = (from sector in DbContext.sectors group sector by sector.TeamId into team_sectors select new InfrStadium(team_sectors.Key, team_sectors.AsQueryable()) ).ToList(); with appropriate constructor: private InfrStadium(int iTeamId, IQueryeable<InfrStadiumSector> eSectors) { IList<Sector> teamSectors = eSectors.ToList(); ... work with data } In this case I've received another but similar error: Expression of type 'System.Int32' cannot be used for parameter of type 'System.Collections.Generic.IEnumerable1[InfrStadiumSector]' of method 'System.Linq.IQueryable1[InfrStadiumSector] AsQueryableInfrStadiumSector' Question 2: Actually, the same question: can't understand at all what is going on here... P.S. I have another to optimize query idea (describe here: Linq2Sql: query optimisation) but I would love to find a solution with 1 request to DB).

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• How to filter what is shown in the for-each loop in XSL

  - by Denoteone

  I thought it would be as easy as tell the for-each to only select top_coach_sales_vw that has "Site" equal to "PB" but when I run the script it does not loop through any of the data in the XML. I am escaping the single quotes because it is part of a php echo. <xsl:for-each select="NewDataSet/top_coach_sales_vw[Site==\'PB\']"> <td><xsl:value-of select="name"/></td> <td><xsl:value-of select="Site"/></td> <td><xsl:value-of select="Status"/></td> </xsl:for-each> XML: <NewDataSet> <top_coach_sales_vw> <name>Mike</name> <Site>PB</Site> <State>Ready</State> </top_coach_sales_vw> <top_coach_sales_vw> <name>Bill</name> <Site>EL</Site> <State>Talking</State> </top_coach_sales_vw> <top_coach_sales_vw> <name>Ted</name> <Site>PB</Site> <State>Ready</State> </top_coach_sales_vw> </NewDataSet>

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• How should I properly format this code?

  - by ct2k7

  Hi, I've a small issue here. I am using an if statement with UIAlertView and I have two situations, both result in UIAlertViews. However, in one situation, I want to dismiss just the UIAlertView, the other, I want the UIAlertView to be dismissed and view to return to root view. This code describes is: if([serverOutput isEqualToString:@"login.true"]){ [Alert dismissWithClickedButtonIndex:0 animated:YES]; [UIApplication sharedApplication].networkActivityIndicatorVisible = NO; UIAlertView *success = [[UIAlertView alloc] initWithTitle:@"Success" message:@"The transaction was a success!" delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil]; [success show]; [success release]; } else { UIAlertView *failure = [[UIAlertView alloc] initWithTitle:@"Failure" message:@"The transaction failed. Contact sales operator!" delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil]; [failure show]; [failure release]; } } -(void)alertView: (UIAlertView *)success clickedButtonAtIndex: (NSInteger)buttonIndex{ switch(buttonIndex) { case 0: { [self.navigationController popToRootViewControllerAnimated:YES]; } } } So, in both cases, they follow the above action, but obviously, that's not what I want. Any ideas on what I do here?

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• Find element all of whose children have a given value

  - by cru3l

  for example, i have this xml <elements> <a> <b>6</b> <b>5</b> <b>6</b> </a> <a> <b>5</b> <b>5</b> <b>6</b> </a> <a> <b>5</b> <b>5</b> <b>5</b> <b>5</b> </a> </elements> i need a xpath query, which must return me parent tag, only if all its children are equal to 5 (a[3] in this case). Something like that //b[text()="5"]/.. but with check of all children's tags. Please note that number of children tags can be different from node to node. It's possible with only xpath query? thanks

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• Coordinating typedefs and structs in std::multiset (C++)

  - by Sarah

  I'm not a professional programmer, so please don't hesitate to state the obvious. My goal is to use a std::multiset container (typedef EventMultiSet) called currentEvents to organize a list of structs, of type Event, and to have members of class Host occasionally add new Event structs to currentEvents. The structs are supposed to be sorted by one of their members, time. I am not sure how much of what I am trying to do is legal; the g++ compiler reports (in "Host.h") "error: 'EventMultiSet' has not been declared." Here's what I'm doing: // Event.h struct Event { public: bool operator < ( const Event & rhs ) const { return ( time < rhs.time ); } double time; int eventID; int hostID; }; // Host.h ... void calcLifeHist( double, EventMultiSet * ); // produces compiler error ... void addEvent( double, int, int, EventMultiSet * ); // produces compiler error // Host.cpp #include "Event.h" ... // main.cpp #include "Event.h" ... typedef std::multiset< Event, std::less< Event > > EventMultiSet; EventMultiSet currentEvents; EventMultiSet * cePtr = &currentEvents; ... Major questions Where should I include the EventMultiSet typedef? Are my EventMultiSet pointers obviously problematic? Is the compare function within my Event struct (in theory) okay? Thank you very much in advance.

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• PDFParsing & extracting the images only in iPhone application.

  - by sagar

  Hello - Every one. ** : My Query : ** I want to extract only images from entire pdf document. ( Using Objective C - for iPhone Application ) : My Efforts : I have gone through this link which has details regarding different operators of PDF Document. ( http://mail-archives.apache.org/mod_mbox/pdfbox-commits/200912.mbox/%[email protected]%3E ) I also studied this document - ( http://developer.apple.com/mac/library/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_pdf_scan/dq_pdf_scan.html#//apple_ref/doc/uid/TP30001066-CH220-TPXREF101 ) I also have gone through entire document of PDFReference.pdf ( From original Adobe Site ) PDFReference.pdf (Adobe Document - says that - for image there are following operators ) q Q BI EI I have placed following table get the image myTable = CGPDFOperatorTableCreate(); CGPDFOperatorTableSetCallback(myTable, "q", arrayCallback2); CGPDFOperatorTableSetCallback(myTable, "TJ", arrayCallback); CGPDFOperatorTableSetCallback(myTable, "Tj", stringCallback); I have following arrayCallback2 method for getting image void arrayCallback2(CGPDFScannerRef inScanner, void *userInfo) { // how to extract image from this code // means I have tried too many different ways. following is incorrect way & not giving image // CGPDFStreamRef stream; // represents a sequence of bytes // if (CGPDFDictionaryGetStream (d, "BI", &stream)){ // CGPDFDataFormat t=CGPDFDataFormatJPEG2000; // CFDataRef data = CGPDFStreamCopyData (stream, &t); // } } above arrayCallback2 method is called for operator "q", But I don't know How to extract the image from it. In short. What should be the solution for extracting the images from the pdf documents? Thanks in advance for your kind help. Sagar kothari.

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• Partial class or "chained inheritance"

  - by Charlie boy

  Hi From my understanding partial classes are a bit frowned upon by professional developers, but I've come over a bit of an issue; I have made an implementation of the RichTextBox control that uses user32.dll calls for faster editing of large texts. That results in quite a bit of code. Then I added spellchecking capabilities to the control, this was made in another class inheriting RichTextBox control as well. That also makes up a bit of code. These two functionalities are quite separate but I would like them to be merged so that I can drop one control on my form that has both fast editing capabilities and spellchecking built in. I feel that simply adding the code form one class to the other would result in a too large code file, especially since there are two very distinct areas of functionality, so I seem to need another approach. Now to my question; To merge these two classes should I make the spellchecking RichTextBox inherit from the fast edit one, that in turn inherits RichTextBox? Or should I make the two classes partials of a single class and thus making them more “equal” so to speak? This is more of a question of OO principles and exercise on my part than me trying to reinvent the wheel, I know there are plenty of good text editing controls out there. But this is just a hobby for me and I just want to know how this kind of solution would be managed by a professional. Thanks!

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• binary_search not working for a vector<string>

  - by VaioIsBorn

  #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main(void) { string temp; vector<string> encrypt, decrypt; int i,n, co=0; cin >> n; for(i=0;i<n;i++) { cin >> temp; encrypt.push_back(temp); } for(i=0;i<n;i++) { cin >> temp; decrypt.push_back(temp); } for(i=0;i<n;i++) { temp = encrypt[i]; if((binary_search(decrypt.begin(), decrypt.end(), temp)) == true) ++co; } cout << co << endl; return 0; } It reads two equal lists of strings and should print out how many of the words in the first list are also found in the second list, simple. Not giving me the expexted results and i think the problem is in binary_search. Can you tell me why ?

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• How do the operators < and > work with pointers?

  - by Øystein

  Just for fun, I had a std::list of const char*, each element pointing to a null-terminated text string, and ran a std::list::sort() on it. As it happens, it sort of (no pun intended) did not sort the strings. Considering that it was working on pointers, that makes sense. According to the documentation of std::list::sort(), it (by default) uses the operator < between the elements to compare. Forgetting about the list for a moment, my actual question is: How do these (, <, =, <=) operators work on pointers in C++ and C? Do they simply compare the actual memory addresses? char* p1 = (char*) 0xDAB0BC47; char* p2 = (char*) 0xBABEC475; e.g. on a 32-bit, little-endian system, p1 p2 because 0xDAB0BC47 0xBABEC475? Testing seems to confirm this, but I thought it'd be good to put it on StackOverflow for future reference. C and C++ both do some weird things to pointers, so you never really know...

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• Adding a button bar at the bottom of ListView upon checkbox select (as in gmail app)??

  - by elto

  I have a ListView with custom adapter. In each row there is a checkbox and couple of textviews. I want user to give option to delete the check marked items, so as soon as soon clicks on one of the checkbox, I want a button bar to slide in from the bottom and stay at the bottom regardless of listview scroll. This is something like the email app behavior of Motorola Cliq and to some extent gmail app itself. I have tried adding a relativelayout (containing buttons) below the listview, which has visibility set to gone initially, but as soon as user checks a button, the visibility changes to "visible". I have added a slide-in animation to it too. It is working but problem is that it is overlapping the last element of the listview which user can not checkmark if the button bar has already become visible. So I tried to set the bottom margin of the listview equal to the height of the button bar when I'm changing the button bar visibility, which solves the problem of overlap, but now the checkbox behavior has gone weird. Clicking on one checkmark tries to checkmark another checkmark in the list for some weird reason. I noticed that this happens because as soon as I change the listview margin, list redraws itself, and during this new call to getView() method of adapter, things mess up. I wanted to ask if anyone has done something like this. What is the best method to add such button bar below list while keeping the slide-in animation intact. Also, What is the footer-view of listview and can that solve my problem?

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• Defining default value in combobox in CakePHP

  - by Keyur

  <?php echo $form->create('admin_merchant_form', array('action' => '#')); echo $form->input('company_name', array('label' => 'Company Name')); echo $form->input('ac_owner', array('label' => 'Account Owner', 'options' => array('a','b','b'), 'default' => $merchant_select)); echo $form->end('Update'); ?> This is CakePHP code to generate a form with one combobox containing the values "a,b,c" and assigning the default value as $merchant_select which is numerical data. Now the problem is when I assign like 'default'=1 it returns 'b' in the combobox as default value but when writing 'default' = $merchant_select the combobox shows only the first value which is 'a'. The $merchant_select variable is assigned a numeric value equal to merchant's id which 1,2 or 3 when I select any row in the grid. And I also have JavaScript code which alerts with the merchant value when I select any row in the grid so the numeric data is definitely assigned to the $merchant_select variable.

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• OpenGL circle rotation

  - by user350632

  I'm using following code to draw my circles: double theta = 2 * 3.1415926 / num_segments; double c = Math.Cos(theta);//precalculate the sine and cosine double s = Math.Sin(theta); double t; double x = r;//we start at angle = 0 double y = 0; GL.glBegin(GL.GL_LINE_LOOP); for(int ii = 0; ii < num_segments; ii++) { float first = (float)(x * scaleX + cx) / xyFactor; float second = (float)(y * scaleY + cy) / xyFactor; GL.glVertex2f(first, second); // output Vertex //apply the rotation matrix t = x; x = c * x - s * y; y = s * t + c * y; } GL.glEnd(); The problem is that when scaleX is different from scaleY then circles are transformed in the right way except for the rotation. In my code sequence looks like this: circle.Scale(tmp_p.scaleX, tmp_p.scaleY); circle.Rotate(tmp_p.rotateAngle); My question is what other calculations should i perform for circle to rotate properly when scaleX and scaleY are not equal?

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• Partitioning data set in r based on multiple classes of observations

  - by Danny

  I'm trying to partition a data set that I have in R, 2/3 for training and 1/3 for testing. I have one classification variable, and seven numerical variables. Each observation is classified as either A, B, C, or D. For simplicity's sake, let's say that the classification variable, cl, is A for the first 100 observations, B for observations 101 to 200, C till 300, and D till 400. I'm trying to get a partition that has 2/3 of the observations for each of A, B, C, and D (as opposed to simply getting 2/3 of the observations for the entire data set since it will likely not have equal amounts of each classification). When I try to sample from a subset of the data, such as sample(subset(data, cl=='A')), the columns are reordered instead of the rows. To summarize, my goal is to have 67 random observations from each of A, B, C, and D as my training data, and store the remaining 33 observations for each of A, B, C, and D as testing data. I have found a very similar question to mine, but it did not factor in multiple variables. I feel silly asking this question because it seems so simple, but I'm stumped. Also, this is my first question on this site, so I apologize in advance for any faux pas on my part.

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• How do I send floats in window messages.

  - by yngvedh

  Hi, What is the best way to send a float in a windows message using c++ casting operators? The reason I ask is that the approach which first occurred to me did not work. For the record I'm using the standard win32 function to send messages: PostWindowMessage(UINT nMsg, WPARAM wParam, LPARAM lParam) What does not work: Using static_cast<WPARAM>() does not work since WPARAM is typedef'ed to UINT_PTR and will do a numeric conversion from float to int, effectively truncating the value of the float. Using reinterpret_cast<WPARAM>() does not work since it is meant for use with pointers and fails with a compilation error. I can think of two workarounds at the moment: Using reinterpret_cast in conjunction with the address of operator: float f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, *reinterpret_cast<WPARAM*>(&f), 0); Using an union: union { WPARAM wParam, float f }; f = 42.0f; ::PostWindowMessage(WM_SOME_MESSAGE, wParam, 0); Which of these are preffered? Are there any other more elegant way of accomplishing this?

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• Avoiding seasonality assumption for stl() or decompose() in R

  - by user303922

  Hello everybody, I have high frequency commodity price data that I need to analyze. My objective is to not assume any seasonal component and just identify a trend. Here is where I run into problems with R. There are two main functions that I know of to analyze this time series: decompose() and stl(). The problem is that they both take a ts object type with a frequency parameter greater than or equal to 2. Is there some way I can assume a frequency of 1 per unit time and still analyze this time series using R? I'm afraid that if I assume frequency greater than 1 per unit time, and seasonality is calculated using the frequency parameter, then my forecasts are going to depend on that assumption. names(crude.data)=c('Date','Time','Price') names(crude.data) freq = 2 win.graph() plot(crude.data$Time,crude.data$Price, type="l") crude.data$Price = ts(crude.data$Price,frequency=freq) I want frequency to be 1 per unit time but then decompose() and stl() don't work! dim(crude.data$Price) decom = decompose(crude.data$Price) win.graph() plot(decom$random[2:200],type="line") acf(decom$random[freq:length(decom$random-freq)]) Thank you.

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• How to check if a number is a power of 2

  - by configurator

  Today I needed a simple algorithm for checking if a number is a power of 2. The algorithm needs to be: Simple Correct for any ulong value. I came up with this simple algorithm: private bool IsPowerOfTwo(ulong number) { if (number == 0) return false; for (ulong power = 1; power > 0; power = power << 1) { // this for loop used shifting for powers of 2, meaning // that the value will become 0 after the last shift // (from binary 1000...0000 to 0000...0000) then, the for // loop will break out if (power == number) return true; if (power > number) return false; } return false; } But then I thought, how about checking if log2x is an exactly round number? But when I checked for 2^63+1, Math.Log returned exactly 63 because of rounding. So I checked if 2 to the power 63 is equal to the original number - and it is, because the calculation is done in doubles and not in exact numbers: private bool IsPowerOfTwo_2(ulong number) { double log = Math.Log(number, 2); double pow = Math.Pow(2, Math.Round(log)); return pow == number; } This returned true for the given wrong value: 9223372036854775809. Does anyone have any suggestion for a better algorithm?

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• [C++] My First Go With Function Templates

  - by bobber205

  Thought it was pretty straight forward. But I get a "iterator not dereferencable" errro when running the below code. What's wrong? template<typename T> struct SumsTo : public std::binary_function<T, T, bool> { int myInt; SumsTo(int a) { myInt = a; } bool operator()(const T& l, const T& r) { cout << l << " + " << r; if ((l + r) == myInt) { cout << " does add to " << myInt; } else { cout << " DOES NOT add to " << myInt; } return true; } }; void main() { list<int> l1; l1.push_back(1); l1.push_back(2); l1.push_back(3); l1.push_back(4); list<int> l2; l2.push_back(9); l2.push_back(8); l2.push_back(7); l2.push_back(6); transform(l1.begin(), l1.end(), l2.begin(), l2.end(), SumsTo<int>(10) ); }

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• C++ Matrix class hierachy

  - by bpw1621

  Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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