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• Finding the specific type held in an ArrayList<Object> (ie. Object = String, etc.)

  - by Christopher Griffith

  Say I have an ArrayList that I have cast to an ArrayList of objects. I know that all the objects that were in the ArrayList I cast were of the same type, but not what the type was. Now, if the ArrayList is not empty, I could take one of the objects in it and use the instanceof operator to learn what the actual type is. But what of the case where the ArrayList is empty? How do I determine what type Object actually is then? Is it possible?

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• How to algorithmically partion a keyspace?

  - by pbhogan

  This is related to consistent hashing and while I conceptually understand what I need to do, I'm having a hard time translating this into code. I'm trying to divide a given keyspace (say, 128 bits) into equal sized partitions. I want the upper bound (highest key) of each partition. Basically, how would I complete this? #define KEYSPACE_BYTE_SIZE 16 #define KEYSPACE_BIT_SIZE (KEYSPACE_BYTE_SIZE * 8) typedef struct _key { char byte[KEYSPACE_BYTE_SIZE]; } key; key * partition_keyspace( int num_partitions ) { key * partitions = malloc( sizeof(key) * num_partitions ); // ... }

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• What is wrong with my version of strchr?

  - by Eduard Saakashvili

  My assignment is to write my own version of strchr, yet it doesn't seem to work. Any advice would be much appreciated. Here it is: char *strchr (const char *s, int c) //we are looking for c on the string s { int dog; //This is the index on the string, initialized as 0 dog = 0; int point; //this is the pointer to the location given by the index point = &s[dog]; while ((s[dog] != c) && (s[dog] != '\0')) { //it keeps adding to dog until it stumbles upon either c or '\0' dog++; } if (s[dog]==c) { return point; //at this point, if this value is equal to c it returns the pointer to that location } else { return NULL; //if not, this means that c is not on the string } }

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• Permutations with extra restrictions

  - by Full Decent

  I have a set of items, for example: {1,1,1,2,2,3,3,3}, and a restricting set of sets, for example {{3},{1,2},{1,2,3},{1,2,3},{1,2,3},{1,2,3},{2,3},{2,3}. I am looking for permutations of items, but the first element must be 3, and the second must be 1 or 2, etc. One such permutation that fits is: {3,1,1,1,2,2,3} Is there an algorithm to count all permutations for this problem in general? Is there a name for this type of problem? For illustration, I know how to solve this problem for certain types of "restricting sets". Set of items: {1,1,2,2,3}, Restrictions {{1,2},{1,2,3},{1,2,3},{1,2},{1,2}}. This is equal to 2!/(2-1)!/1! * 4!/2!/2!. Effectively permuting the 3 first, since it is the most restrictive and then permuting the remaining items where there is room.

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• C++ template specialization

  - by user231536

  I have a class template <typename T> class C { static const int K=1; static ostream& print(ostream& os, const T& t) { return os << t;} }; I would like to specialize C for int. //specialization for int template <> C<int>{ static const int K=2; } I want the default print method that works for int to remain and just change the constant. For some specializations, I want to keep K=1 and change the print method because there is no << operator. How do I do this?

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• What is the difference between "a is b" and "id(a) == id(b)" in Python?

  - by bp

  The id() inbuilt function gives... an integer (or long integer) which is guaranteed to be unique and constant for this object during its lifetime. The is operator, instead, gives... object identity So why is it possible to have two objects that have the same id but return False to an is check? Here is an example: >>> class Test(): ... def test(): ... pass >>> a = Test() >>> b = Test() >>> id(a.test) == id(b.test) True >>> a.test is b.test False A more troubling example: (continuing the above) >>> b = a >>> b is a True >>> b.test is a.test False >>> a.test is a.test False

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• Disabled Select drop down checking through PHP

  - by user541597

  I have a couple of drop down boxes I access through POST with PHP. When the boxes are disabled and not equal to zero I have the program do something. However when they are disabled I do not want them to do anything. The way I check if the boxes are active is by using an if statement if ($_POST['box'] != "blank"){ //do something } So basically I check if the box is not in the default blank position run the if statement. However when it is disabled I am not sure how to check or what kind of value it returns if any. What can I add to the if statement so it will not go into the loop when the boxes are disabled? I tried: if ($_POST['box'] != "blank" || $_POST['box'] != ""){ //do something } But that did not work. Any ideas?

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• Postfix evaluation in C

  - by Andrewziac

  I’m taking a course in C and we have to make a program for the classic Postfix evaluation problem. Now, I’ve already completed this problem in java, so I know that we have to use a stack to push the numbers into, then pop them when we get an operator, I think I’m fine with all of that stuff. The problem I have been having is scanning the postfix expression in C. In java it was easier because you could use charAt and you could use the parseInt command. However, I’m not aware of any similar commands in C. So could anyone explain a method to read each value from a string in the form: 4 9 * 0 - = Where the equals is the signal of the end of the input. Any help would be greatly appreciated and thank you in advance :)

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• Calculating a parabola: What am I doing wrong? [closed]

  - by Nils

  I was following this thread and copied the code in my project. Playing around with it turns out that it seems not to be very precise. Recall the formula: y = ax^2 + bx +c Since the first given point I have is at x1 = 0, we already have c=y1 . We just need to find a and b. Using: y2 = ax2^2 + bx2 +c y3 = ax3^2 + bx3 +c Solving the equations for b yields: b = y/x - ax - cx Now setting both equations equal to each other so b falls out y2/x2 - ax2 - cx2 = y3/x3 - ax3 - cx3 Now solving for a gives me: a = ( x3*(y2 - c) + x2*(y3 - c) ) / ( x2*x3*(x2 - x3) ) (is that correct?!) And then using again b = y2/x2 - ax2 - cx2 to find b. However so far I haven't found the correct a and b coeffs. What am I doing wrong?

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• Switching from php to python

  - by ts

  Hello I am trying to make a list of things which can be difficult/surprising to someone who is changing language from PHP to Python. so far i have rather short list: forget require / include, learn import (this was most difficult to me - to understand package - module - class - object hierarchy and its mapping to filesystem) you can't just upload file on server to have webpage (-mod_python, wsgi etc) learn the python way for use variable class names (new $class() vs import + getattr) / operator in python 2.x and all float-related horrors those were difficult to me, it takes few days before mind adapts a new paradigm after i found that there is few other areas which could be challenging for someone with (too) many years of php: everything is an object you have to live with exceptions array vs list, set, dictionary, tuple ... learn (effective) list comprehensions learn generators any other ideas / personal experiences ?

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• data loading - app launching on tableview

  - by wallou

  hi, i encounter an issue with my application. On one hand when my app launches, the first view displayed is a tableview within a tableviewcontroller. On the other hand my app calls a web service to collect data. These methods are in MyAppDelegate\applicationDidFinishLaunching. The thing is that my tableview is made of custom cells that need data from the web service. I noticed that the view (with the tableview) is launched first and then MyAppDelegate\applicationDidFinishLaunchin is executed. As a result the labels of my custom cells are all equal to null as my arrays aren't filled yet by the web service. I would like to know the proper way to make it. If anyone has an idea please tell me. Wallou

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• How to check if the sum of some records equals the difference between two other records in t-sql?

  - by Dan Appleyard

  I have a view that contains bank account activity. ACCOUNT BALANCE_ROW AMOUNT SORT_ORDER 111 1 0.00 1 111 0 10.00 2 111 0 -2.50 3 111 1 7.50 4 222 1 100.00 5 222 0 25.00 6 222 1 125.00 7 ACCOUNT = account number BALANCE_ROW = either starting or ending balance would be 1, otherwise 0 AMOUNT = the amount SORT_ORDER = simple order to return the records in the order of start balance, activity, and end balance I need to figure out a way to see if the sum of the non balance_row rows equal the difference between the ending balance and the starting balance. The result for each account (1 for yes, 0 for no) would be simply added to the resulting result set. Example: Account 111 had a starting balance of 0.00. There were two account activity records of 10.00 and -2.5. That resulted in the ending balance of 7.50. I've been playing around with temp tables, but I was not sure if there is a more efficient way of accomplishing this. Thanks for any input you may have!

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• Quickest way to compute the number of shared elements between two vectors

  - by shn

  Suppose I have two vectors of the same size vector< pair<float, NodeDataID> > v1, v2; I want to compute how many elements from both v1 and v2 have the same NodeDataID. For example if v1 = {<3.7, 22>, <2.22, 64>, <1.9, 29>, <0.8, 7>}, and v2 = {<1.66, 7>, <0.03, 9>, <5.65, 64>, <4.9, 11>}, then I want to return 2 because there are two elements from v1 and v2 that share the same NodeDataIDs: 7 and 64. What is the quickest way to do that in C++ ? Just for information, note that the type NodeDataIDs is defined as I use boost as: typedef adjacency_list<setS, setS, undirectedS, NodeData, EdgeData> myGraph; typedef myGraph::vertex_descriptor NodeDataID; But it is not important since we can compare two NodeDataID using the operator == (that is, possible to do v1[i].second == v2[j].second)

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• compare two characters based on subset

  - by schultem

  I have a simple dataframe with two columns: df <- data.frame(x = c(1,1,2,2,3), y = c(rep(1:2,2),1), target = c('a','a','a','b','a')) I would like to compare the strings in the target column (find out whether they are equal or not, i.e., TRUE or FALSE) within every level of x (same number for x). First I would like to compare lines 1 and 2, then 3 and 4 ... My problem is that I am missing some comparisons, for example, line 5 has only one case instead of two - so it should turn out to be FALSE. Variable y indicates the first and second case within x. I played around with ddply doing something like: ddply(df, .(x), summarise, ifelse(as.character(df[df$y == '1',]$target), as.character(df[df$y == '2',]$target),0,1)) which is ugly ... and does not work ... Any insights how I could achieve this comparison? Thanks

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• C++ Reference of vector

  - by void

  Hello, class Refvect { public: vector<int> &refv; Refvect(int t, vector<int> &refv = vector<int>()) : refv(refv) { }; void operator()() { refv.clear(); } }; int main () { Refvect r(0); r(); } With Visual Studio 2010, this gives me an error : "vector iterators incompatible" at the execution, but I don't understand why (but I can insert elements in refv without any problem). The temporary object vector() lives as long as the reference, no?

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• Label field problem in the treenode Tag. (Struts2/Ajax)

  - by ryan

  I'm using struts as a framework for a web-app. The following code runs inside a loop where I access the database to retrieve values to be used as nodes for a tree. <s:set name="categoryValue" value= "%{'<%=rs.getString("category")%>'}"> </s:set> <sx:treenode id="child1" label ="%{#categoryValue}"/> The error I get is "/jsp/tree.jsp(249,65) equal symbol expected" However if i give <s:set name="categoryValue" value= "%{'Test'}"> the value Test is obtained. Can anyone tell me how to set the value of the 'label' with strings?

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• Calling function from an object with event listener

  - by Mirat Can Bayrak

  i have a view model something like this: CANVAS = getElementById... RemixView = function(attrs) { this.model = attrs.model; this.dragging = false; this.init(); }; RemixView.prototype = { init: function() { CANVAS.addEventListener("click", this.handleClick); }, handleClick: function(ev) { var obj = this.getHoveredObject(ev); }, getHoveredObject: function(ev) {} ... ... } rv = new RemixView() the problem is my when clickHandler event fired, this object is being equal to CANVAS object, not RemixView. So i get error that says: this.getHoveredObject is not a function What is correct approach at that stuation?

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• .NET Garbage Collection behavior (with DataTable)

  - by gmac

  I am wonder why after creating a very simple DataTable and then setting it to null why Garbage Collection does not clear out all the memory used by that DataTable. Here is an example. The variable Before should be equal to Removed but it is not. { long Before = 0, After = 0, Removed = 0, Collected = 0; Before = GC.GetTotalMemory(true); DataTable dt = GetSomeDataTableFromSql(); After = GC.GetTotalMemory(true); dt = null; Removed = GC.GetTotalMemory(true); GC.Collect(); Collected = GC.GetTotalMemory(true); } Gives the following results. Before = 388116 After = 731248 Removed = 530176 Collected = 530176

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• How do I create a timed ban on an account? (PHP/mysql)

  - by ggfan

  I want to create a function that allows me to ban an account for 10days. In the dbc, I have a field called "ban" and Boolean of 1=notban, 0=ban. I also have a field called "date_banned" which is just the timestamp of when the user got banned. My question is how do I create a time frame of 10days from the date the user was banned? ex: James was banned on "2010-05-03 20:43:48". So how can I go about adding 10days to the timestamp? And after 10days, it would set the "ban" equal to 1(which is not banned).

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• Can't compile std::map sorting, why?

  - by Vincenzo

  This is my code: map<string, int> errs; struct Compare { bool operator() (map<string, int>::const_iterator l, map<string, int>::const_iterator r) { return ((*l).second < (*r).second); } } comp; sort(errs.begin(), errs.end(), comp); Can't compile. This is what I'm getting: no matching function for call to ‘sort(..’ Why so? Can anyone help? Thanks!

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• Problem decrementing in Java with '-='

  - by hanesjw

  I'm making a scrolling game on Android and am having a hard time figuring out why the code below does not decrement past 0. Objects start at the end of the screen (so the x position is equal to the width of the screen) the objects move accross the screen by decrementing their x positions. I want them to scroll off of the screen, but when the x position hits 0, the objects just stay at 0, they do not move into the negatives. Here is my code to move objects on the screen private void incrementPositions(long delta) { float incrementor = (delta / 1000F) * Globals.MAP_SECTION_SPEED; for(Map.Entry<Integer, HashMap<Integer, MapSection>> column : scrollingMap.entrySet()) { for(Map.Entry<Integer, MapSection> row : column.getValue().entrySet()) { MapSection section = row.getValue(); section.x -= incrementor; } } } It works ok if I change section.x -= incrementor; to section.x = section.x - (int)incrementor; but if i do that the scrolling doesn't appear as smooth.

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• Javascript function not working with an array

  - by Ryan Harvie

  Hi, i have this function which loops through an array of check boxes checking if the boxes value is equal to something in a text box, i dont know whats wrong. function checkValue(contain) { var boxes = document.getElementsByTagName("input"); for (var i = 0; i < boxes.length; i++) { if (boxes[i].name == "vote[]") { if (boxes[i].value.indexOf(contain.value) != -1) { boxes[i].checked = true; } } } } and this is how i call it OnClick="uncheckAll(); checkValue(document.getElementsByName("countrylist"));" this code is in side a echo in php which is like this echo ' ';

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• How to check null element if it is integer array in Java?

  - by masato-san

  I'm quite new to Java and having an issue checking null element in integer array. I'm using Eclipse for editor and the line that checks null element is showing error: Line that complains: if(a[i] != null) { Error msg from Eclipse: The operator != is undefined for the argument type(s) int, null In PHP, this works without any problem but in Java it seems like I have to change the array type from integer to Object to make the line not complain (like below) Object[] a = new Object[3]; So my question is if I still want to declare as integer array and still want to check null, what is the syntax for it? Code: public void test() { int[] a = new int[3]; for(int i=0; i<a.length; i++) { if(a[i] != null) { //this line complains... System.out.println('null!'); } } }

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• Double "!!" in Ruby [closed]

  - by Alex Maslakov

  Possible Duplicate: What does !! mean in ruby? Ruby, !! operator (a/k/a the double-bang) Sometimes I see a Ruby code like this def sent? !!@sent_at end It seems to be not logical. Is it necessary to use here double !? As far as I'm concerned, it might be just def sent? @sent_at end UPDATE: then what is the difference between these def sent? !!@sent_at end def sent? @sent_at.nil? end def sent? @sent_at == nil end

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• Implementing an iterator over binary tree using C++ 11

  - by user1459339

  I would like to create an iterator over the binary tree so as to be able to use range-based for loop. I understand I ought to implement the begin() and end() function first. Begin should probably point to the root. According to the specification, however, the end() functions returns "the element following the last valid element". Which element (node) is that? Would it not be illegal to point to some "invalid" place? The other thing is the operator++. What is the best way to return "next" element in tree? I just need some advice to begin with this programming.

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