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• Iterables.find and Iterators.find - instead of throwing exception, get null

  - by mjlee

  I'm using google-collections and trying to find the first element that satisfies Predicate if not, return me 'null'. Unfortunately, Iterables.find and Iterators.find throws NoSuchElementException when no element is found. Now, I am forced to do Object found = null; if ( Iterators.any( newIterator(...) , my_predicate ) { found = Iterators.find( newIterator(...), my_predicate ) } I can surround by 'try/catch' and do the same thing but for my use-cases, I am going to encounter many cases where no-element is found. Is there a simpler way of doing this?

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• C# dictionary and lookup add / update

  - by freddy smith

  I am sick of doing blocks of code like this for various bits of code I have: if (dict.ContainsKey[key]) { dict[key] = value; } else { dict.Add(key,value); } and for lookups (i.e. key - list of value) if (lookup.ContainsKey[key]) { lookup[key].Add(value); } else { lookup.Add(new List); lookup[key].Add(value); } Is there another collections lib or extension method I should use to do this in one line of code no matter what the key and value types are? e.g. dict.AddOrUpdate(key,value) lookup.AddOrUpdate(key,value)

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• Shortcut for adding to List in a HashMap

  - by Damo

  I often have a need to take a list of objects and group them into a Map based on a value contained in the object. Eg. take a list of Users and group by Country. My code for this usually looks like: Map<String, List<User>> usersByCountry = new HashMap<String, List<User>>(); for(User user : listOfUsers) { if(usersByCountry.containsKey(user.getCountry())) { //Add to existing list usersByCountry.get(user.getCountry()).add(user); } else { //Create new list List<User> users = new ArrayList<User>(1); users.add(user); usersByCountry.put(user.getCountry(), users); } } However I can't help thinking that this is awkward and some guru has a better approach. The closest I can see so far is the MultiMap from Google Collections. Are there any standard approaches? Thanks!

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• How can I create a collection of references in C#

  - by Jonathan Kaufman

  Ok I am having a cross language hiccup. In C# with it's great collections like List and I have: a Map class with properties of: List<byte[]> Images; List<Tile> Tiles; a Tile Class of: byte[] ImageData; int X; int Y; Now I want to add an image to the Map class and have the ImageData property of the Tile Classes to "reference" it. I have discovered I can't just assign it Images[0]. You can't have a reference to an object of a List. My fix was to create a Dictionary. Is this the best way or can I somehow have a "pointer" to a collection of objects?

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• C# - implementing GetEnumerator() for a collection inherited from List<string>

  - by Vojtech

  Hi, I am trying to implement FilePathCollection. Its items would be simple file names (without a path - such as "image.jpg"). Once the collection is used via foreach cycle, it should return the full path created by concatenating with "baseDirectory". How can I do that? public class FilePathCollection : List<string> { string baseDirectory; public FileCollection(string baseDirectory) { this.baseDirectory = baseDirectory; } new public System.Collections.IEnumerator GetEnumerator() { foreach (string value in this._list) //this does not work because _list is private yield return baseDirectory + value; } } Thanks in advance! :-)

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• Subtracting two lists in Python

  - by wich

  In Python, How can one subtract two non-unique, unordered lists? Say we have a = [0,1,2,1,0] and b = [0, 1, 1] I'd like to do something like c = a - b and have c be [2, 0] or [0, 2] order doesn't matter to me. This should throw an exception if a does not contain all elements in b. Note this is different from sets! I'm not interested in finding the difference of the sets of elements in a and b, I'm interested in the difference between the actual collections of elements in a and b. I can probably work this out with a for loop, looking up the first element of b in a and then removing the element from b and from a, etc. But this doesn't appeal to me, I'd like to do this with list comprehension in a nice and easy way. Is this possible?

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• Is there a good collection library for C-language?

  - by matti

  We have to maintain and even develop C-code of our legacy system. Is there good collection library that would support Java/C# (new versions) style collections. Hashtable, HashSet, etc. Of course without objects, but with structs. The HashTable key limitations to "strings" and ints is not a problem. It wouldn't be bad if it's free even for commercial use. I'm back to C from C# and I must say i'm depressed using our own libraries and the language in general. We're using VS2005 and MS C-compiler if that has nothing to do with anything. Thanks & BR -Matti

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• Java List Sorting: Is there a way to keep a list permantly sorted automatically like TreeMap?

  - by david

  In Java you can build up an ArrayList with items and then call: Collections.sort(list, comparator); Is there anyway to pass in the Comparator at the time of List creation like you can do with TreeMap? The goal is to be able add an element to the list and instead of having it automatically appended to the end of the list, the list would keep itself sorted based on the Comparator and insert the new element at the index determined by the Comparator. So basically the list might have to re-sort upon every new element added. Is there anyway to achieve this in this way with the Comparator or by some other similar means? Thanks.

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• Using Custom Generic Collection faster with objects than List

  - by Kaminari

  I'm iterating through a List<> to find a matching element. The problem is that object has only 2 significant values, Name and Link (both strings), but has some other values which I don't want to compare. I'm thinking about using something like HashSet (which is exactly what I'm searching for -- fast) from .NET 3.5 but target framework has to be 2.0. There is something called Power Collections here: http://powercollections.codeplex.com/, should I use that? But maybe there is other way? If not, can you suggest me a suitable custom collection?

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• 2 compareTo method overriden in the same class definition, how could I force to use the second?

  - by jayjaypg22

  I want to sort a list List<Blabla> donnees by a criterion on one of its field. My problem is that compareTo is already overriden for this Class. So I've got something like : Blabla { public int compareTo(Object other) { ... } public int compareTo(Blabla other) { ... } } In a business layer class I call : Business { method (){ Collections.sort(List<Blabla > donnees); } } But this call N°1 compareTo method with object parameter. How could I sort my list with the N°2 method?

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• C#, Using Custom Generic Collection faster with objects than List

  - by Kaminari

  Hello, I'm using for now List< to iterate through some object collection and find matching element, The problem is that object has only 2 significant values Name and Link (strings) but has some other values wich I dont want to compare. I'm thinkig about using something like HashSet (wich is exactly what I'm searching for - fast) from .NET 3.5 but target framework has to be 2.0. There is something called Power Collections here: http://powercollections.codeplex.com/ But maybe there is other way? If not, can you suggest me a suitable custom collection?

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• Is map/collection order stable between calls?

  - by John

  If I have a hash map and iterate over the objects repeatedly, is it correct that I'm not guaranteed the same order for every call? For example, could the following print two lines that differ from each other: Map<String,Integer> map = new HashMap<String,Integer>() {{ put("a", 1); put("b", 2); put("c", 3); }}; System.out.println(map); System.out.println(map); And is this the case for sets and collections in general? If so, what's the best way in case you have to iterate twice over the same collection in the same order (regardless of what order that is)? I guess converting to a list.

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• Output of Iterable.sliding as Tuple

  - by ziggystar

  The method sliding on collections returns a sliding window of given size in the form of X[Iterable[A]] with X being the type of the collection and A the element type. Often I need two or three elements and I prefer to have them named. One ugly workaround for sliding(2) is the following: points.sliding(2).foreach{ twoPoints => val (p1,p2) = (twoPoints.head,twoPoints.last) //do something } This sucks and only works for two elements. Also note that (a,b) = (twoPoints(0),twoPoints(1)) doesn't work. Help me!

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• Why would you use a MyObject[] internally, but expose a List<MyObject>?

  - by timmyd

  I have come across a class that has an immutable property: MyObject[] allObjs The property is initialized like this: List<MyObject> objs = createAllMyObjects(); allObjs = objs.toArray(new MyObject[objs.size()]); When it is exposed through the accessor, it's done as a List: public List<MyObject> getAllMyObjects() { return Collections.unmodifiableList(Arrays.asList(allObjs)); } Why would a programmer do this? Is there a benefit that I don't know about? Performance is not a concern, as the array of objs will only ever number in a few dozen elements. It seems that we are going round and round in circles. The class is a sort of factory, so it's got a private constructor and exposes only static methods (not sure if this could be a reason for the madness).

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• Oracle E-Business Financials Recommended Patch Collections (RPCs) for R12.1.3 Have Been Released for August 2012

  - by Oracle_EBS

  What is a Recommended Patch Collection (RPC)? An RPC is a collection of recommended patches consolidated into a single, downloadable patch, ready to be applied. The RPCs are created with the following goals in mind: Stability: Address issues that occur often and interfere with the normal completion of crucial business processes, such as period close--as observed by Oracle Development and Global Customer Support. Root Cause Fixes: Deliver a root cause fix for data corruption issues that delay period close, normal transaction flow actions, performance, and other issues. Compact: While bundling a large number of important corrections, we have kept the file footprint as small as possible to facilitate uptake and minimize testing. Reliable: Reliable code with multiple customer downloads and comprehensive testing by QA, Support and Proactive Support. RPCs are available for the following products: Cash Management Collections E-Business Tax Financials for India Fixed Assets General Ledger Internet Expenses iReceivables Loans Payables Payments Receivables Subledger Accounting For the latest Financials Recommended Patch Collections (RPCs), please view: EBS: R12.1 Oracle Financials Recommended Patches [Doc ID 954704.1].

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• Sorting in Hash Maps in Java

  - by Crystal

  I'm trying to get familiar with Collections. I have a String which is my key, email address, and a Person object (firstName, lastName, telephone, email). I read in the Java collections chapter on Sun's webpages that if you had a HashMap and wanted it sorted, you could use a TreeMap. How does this sort work? Is it based on the compareTo() method you have in your Person class? I overrode the compareTo() method in my Person class to sort by lastName. But it isn't working properly and was wondering if I have the right idea or not. getSortedListByLastName at the bottom of this code is where I try to convert to a TreeMap. Also, if this is the correct way to do it, or one of the correct ways to do it, how do I then sort by firstName since my compareTo() is comparing by lastName. import java.util.*; public class OrganizeThis { /** Add a person to the organizer @param p A person object */ public void add(Person p) { staff.put(p.getEmail(), p); //System.out.println("Person " + p + "added"); } /** * Remove a Person from the organizer. * * @param email The email of the person to be removed. */ public void remove(String email) { staff.remove(email); } /** * Remove all contacts from the organizer. * */ public void empty() { staff.clear(); } /** * Find the person stored in the organizer with the email address. * Note, each person will have a unique email address. * * @param email The person email address you are looking for. * */ public Person findByEmail(String email) { Person aPerson = staff.get(email); return aPerson; } /** * Find all persons stored in the organizer with the same last name. * Note, there can be multiple persons with the same last name. * * @param lastName The last name of the persons your are looking for. * */ public Person[] find(String lastName) { ArrayList<Person> names = new ArrayList<Person>(); for (Person s : staff.values()) { if (s.getLastName() == lastName) { names.add(s); } } // Convert ArrayList back to Array Person nameArray[] = new Person[names.size()]; names.toArray(nameArray); return nameArray; } /** * Return all the contact from the orgnizer in * an array sorted by last name. * * @return An array of Person objects. * */ public Person[] getSortedListByLastName() { Map<String, Person> sorted = new TreeMap<String, Person>(staff); ArrayList<Person> sortedArrayList = new ArrayList<Person>(); for (Person s: sorted.values()) { sortedArrayList.add(s); } Person sortedArray[] = new Person[sortedArrayList.size()]; sortedArrayList.toArray(sortedArray); return sortedArray; } private Map<String, Person> staff = new HashMap<String, Person>(); public static void main(String[] args) { OrganizeThis testObj = new OrganizeThis(); Person person1 = new Person("J", "W", "111-222-3333", "[email protected]"); Person person2 = new Person("K", "W", "345-678-9999", "[email protected]"); Person person3 = new Person("Phoebe", "Wang", "322-111-3333", "[email protected]"); Person person4 = new Person("Nermal", "Johnson", "322-342-5555", "[email protected]"); Person person5 = new Person("Apple", "Banana", "123-456-1111", "[email protected]"); testObj.add(person1); testObj.add(person2); testObj.add(person3); testObj.add(person4); testObj.add(person5); System.out.println(testObj.findByEmail("[email protected]")); System.out.println("------------" + '\n'); Person a[] = testObj.find("W"); for (Person p : a) System.out.println(p); System.out.println("------------" + '\n'); a = testObj.find("W"); for (Person p : a) System.out.println(p); System.out.println("SORTED" + '\n'); a = testObj.getSortedListByLastName(); for (Person b : a) { System.out.println(b); } } } Person class: public class Person implements Comparable { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName) { this.firstName = firstName; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getTelephone() { return telephone; } public void setTelephone(String telephone) { this.telephone = telephone; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public int compareTo(Object o) { String s1 = this.lastName + this.firstName; String s2 = ((Person) o).lastName + ((Person) o).firstName; return s1.compareTo(s2); } public boolean equals(Object otherObject) { // a quick test to see if the objects are identical if (this == otherObject) { return true; } // must return false if the explicit parameter is null if (otherObject == null) { return false; } if (!(otherObject instanceof Person)) { return false; } Person other = (Person) otherObject; return firstName.equals(other.firstName) && lastName.equals(other.lastName) && telephone.equals(other.telephone) && email.equals(other.email); } public int hashCode() { return this.email.toLowerCase().hashCode(); } public String toString() { return getClass().getName() + "[firstName = " + firstName + '\n' + "lastName = " + lastName + '\n' + "telephone = " + telephone + '\n' + "email = " + email + "]"; } }

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• Sorting and Re-arranging List of HashMaps

  - by HonorGod

  I have a List which is straight forward representation of a database table. I am trying to sort and apply some magic after the data is loaded into List of HashMaps. In my case this is the only hard and fast way of doing it becoz I have a rules engine that actually updates the values in the HashMap after several computations. Here is a sample data representation of the HashMap (List of HashMap) - {fromDate=Wed Mar 17 10:54:12 EDT 2010, eventId=21, toDate=Tue Mar 23 10:54:12 EDT 2010, actionId=1234} {fromDate=Wed Mar 17 10:54:12 EDT 2010, eventId=11, toDate=Wed Mar 17 10:54:12 EDT 2010, actionId=456} {fromDate=Sat Mar 20 10:54:12 EDT 2010, eventId=20, toDate=Thu Apr 01 10:54:12 EDT 2010, actionId=1234} {fromDate=Wed Mar 24 10:54:12 EDT 2010, eventId=22, toDate=Sat Mar 27 10:54:12 EDT 2010, actionId=1234} {fromDate=Wed Mar 17 10:54:12 EDT 2010, eventId=11, toDate=Fri Mar 26 10:54:12 EDT 2010, actionId=1234} {fromDate=Sat Mar 20 10:54:12 EDT 2010, eventId=11, toDate=Wed Mar 31 10:54:12 EDT 2010, actionId=1234} {fromDate=Mon Mar 15 10:54:12 EDT 2010, eventId=12, toDate=Wed Mar 17 10:54:12 EDT 2010, actionId=567} I am trying to achieve couple of things - 1) Sort the list by actionId and eventId after which the data would look like - {fromDate=Wed Mar 17 10:54:12 EDT 2010, eventId=11, toDate=Wed Mar 17 10:54:12 EDT 2010, actionId=456} {fromDate=Mon Mar 15 10:54:12 EDT 2010, eventId=12, toDate=Wed Mar 17 10:54:12 EDT 2010, actionId=567} {fromDate=Wed Mar 24 10:54:12 EDT 2010, eventId=22, toDate=Sat Mar 27 10:54:12 EDT 2010, actionId=1234} {fromDate=Wed Mar 17 10:54:12 EDT 2010, eventId=21, toDate=Tue Mar 23 10:54:12 EDT 2010, actionId=1234} {fromDate=Sat Mar 20 10:54:12 EDT 2010, eventId=20, toDate=Thu Apr 01 10:54:12 EDT 2010, actionId=1234} {fromDate=Wed Mar 17 10:54:12 EDT 2010, eventId=11, toDate=Fri Mar 26 10:54:12 EDT 2010, actionId=1234} {fromDate=Sat Mar 20 10:54:12 EDT 2010, eventId=11, toDate=Wed Mar 31 10:54:12 EDT 2010, actionId=1234} 2) If we group the above list by actionId they would be resolved into 3 groups - actionId=1234, actionId=567 and actionId=456. Now here is my question - For each group having the same eventId, I need to update the records so that they have wider fromDate to toDate. Meaning, if you consider the last two rows they have same actionId = 1234 and same eventId = 11. Now we can to pick the least fromDate from those 2 records which is Wed Mar 17 10:54:12 and farther toDate which is Wed Mar 31 10:54:12 and update those 2 record's fromDate and toDate to Wed Mar 17 10:54:12 and Wed Mar 31 10:54:12 respectively. Any ideas? PS: I already have some pseudo code to start with. import java.util.ArrayList; import java.util.Calendar; import java.util.Collections; import java.util.Comparator; import java.util.Date; import java.util.HashMap; import java.util.List; import org.apache.commons.lang.builder.CompareToBuilder; public class Tester { boolean ascending = true ; boolean sortInstrumentIdAsc = true ; boolean sortEventTypeIdAsc = true ; public static void main(String args[]) { Tester tester = new Tester() ; tester.printValues() ; } public void printValues () { List<HashMap<String,Object>> list = new ArrayList<HashMap<String,Object>>() ; HashMap<String,Object> map = new HashMap<String,Object>(); map.put("actionId", new Integer(1234)) ; map.put("eventId", new Integer(21)) ; map.put("fromDate", getDate(1) ) ; map.put("toDate", getDate(7) ) ; list.add(map); map = new HashMap<String,Object>(); map.put("actionId", new Integer(456)) ; map.put("eventId", new Integer(11)) ; map.put("fromDate", getDate(1)) ; map.put("toDate", getDate(1) ) ; list.add(map); map = new HashMap<String,Object>(); map.put("actionId", new Integer(1234)) ; map.put("eventId", new Integer(20)) ; map.put("fromDate", getDate(4) ) ; map.put("toDate", getDate(16) ) ; list.add(map); map = new HashMap<String,Object>(); map.put("actionId", new Integer(1234)) ; map.put("eventId", new Integer(22)) ; map.put("fromDate",getDate(8) ) ; map.put("toDate", getDate(11)) ; list.add(map); map = new HashMap<String,Object>(); map.put("actionId", new Integer(1234)) ; map.put("eventId", new Integer(11)) ; map.put("fromDate",getDate(1) ) ; map.put("toDate", getDate(10) ) ; list.add(map); map = new HashMap<String,Object>(); map.put("actionId", new Integer(1234)) ; map.put("eventId", new Integer(11)) ; map.put("fromDate",getDate(4) ) ; map.put("toDate", getDate(15) ) ; list.add(map); map = new HashMap<String,Object>(); map.put("actionId", new Integer(567)) ; map.put("eventId", new Integer(12)) ; map.put("fromDate", getDate(-1) ) ; map.put("toDate",getDate(1)) ; list.add(map); System.out.println("\n Before Sorting \n "); for(int j = 0 ; j < list.size() ; j ++ ) System.out.println(list.get(j)); Collections.sort ( list , new HashMapComparator2 () ) ; System.out.println("\n After Sorting \n "); for(int j = 0 ; j < list.size() ; j ++ ) System.out.println(list.get(j)); } public static Date getDate(int days) { Calendar cal = Calendar.getInstance(); cal.setTime(new Date()); cal.add(Calendar.DATE, days); return cal.getTime() ; } public class HashMapComparator2 implements Comparator { public int compare ( Object object1 , Object object2 ) { if ( ascending == true ) { return new CompareToBuilder() .append(( ( HashMap ) object1 ).get ( "actionId" ), ( ( HashMap ) object2 ).get ( "actionId" )) .append(( ( HashMap ) object2 ).get ( "eventId" ), ( ( HashMap ) object1 ).get ( "eventId" )) .toComparison(); } else { return new CompareToBuilder() .append(( ( HashMap ) object2 ).get ( "actionId" ), ( ( HashMap ) object1 ).get ( "actionId" )) .append(( ( HashMap ) object2 ).get ( "eventId" ), ( ( HashMap ) object1 ).get ( "eventId" )) .toComparison(); } } } }

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• Compiling Java code in terminal having a Jar in CLASSPATH

  - by Masi

  How can you compile the code using javac in a terminal by using google-collections in CLASSPATH? Example of code trying to compile using javac in a terminal (works in Eclipse) import com.google.common.collect.BiMap; import com.google.common.collect.HashBiMap; public class Locate { ... BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ... } Compiling in terminal src 288 % javac Locate.java Locate.java:14: package com.google.common.collect does not exist import com.google.common.collect.BiMap; ^ Locate.java:15: package com.google.common.collect does not exist import com.google.common.collect.HashBiMap; ^ Locate.java:153: cannot find symbol symbol : class BiMap location: class Locate BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ^ Locate.java:153: cannot find symbol symbol : variable HashBiMap location: class Locate BiMap<MyFile, Integer> rankingToResult = HashBiMap.create(); ^ 4 errors My CLASSPATH src 289 % echo $CLASSPATH /u/1/bin/javaLibraries/google-collect-1.0.jar

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• Synchronizing a collection of wrapped objects with a collection of unwrapped objects

  - by Kenneth Cochran

  I have two classes: Employee and EmployeeGridViewAdapter. Employee is composed of several complex types. EmployeeGridViewAdapter wraps a single Employee and exposes its members as a flattened set of system types so a DataGridView can handle displaying, editing, etc. I'm using VS's builtin support for turning a POCO into a data source, which I then attach to a BindingSource object. When I attach the DataGridView to the BindingSource it creates the expected columns and at runtime I can perform the expected CRUD operations. All is good so far. The problem is the collection of adapters and the collection of employees aren't being synchronized. So all the employees I create an runtime never get persisted. Here's a snippet of the code that generates the collection of EmployeeGridViewAdapter's: var employeeCollection = new List<EmployeeGridViewAdapter>(); foreach (var employee in this.employees) { employeeCollection.Add(new EmployeeGridViewAdapter(employee)); } this.view.Employees = employeeCollection; Pretty straight forward but I can't figure out how to synchronize changes back to the original collection. I imagine edits are already handled because both collections reference the same objects but creating new employees and deleting employees aren't happening so I can't be sure.

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• Explaining verity index and document search limits

  - by Ahmad

  As present, we currently have a CF8 standard edition server which have some limitations around verity indexing. According to Adobe Verity Server has the following document search limits (limits are for all collections registered to Verity Server): - 10,000 documents for ColdFusion Developer Edition - 125,000 documents for ColdFusion Standard Edition - 250,000 documents for ColdFusion Enterprise Edition We have now reached a stage where the server wide number of documents indexed exceed 125k. However, the largest verity collection consists of about 25k documents(and this is expected to grow). Only one collection is ever searched at a time. In my understanding, this means that I can still search an entire collection with no restrictions. Is this correct? Or does it mean that only documents that were indexed across all collection prior to reaching the limit are actually searchable? We are considering moving to CF9 standard as a solution to this and to use the Solr solution which has no restrictions. The coldfusionjedi highlights some differences between Verity and Solr. However, before we upgrade I am trying to gain a clearer understanding of this before we commit to an upgrade. Can someone provide me a clear explanation as to what this means and how it actually affects verity searching and indexing?

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• A map and set which uses contiguous memory and has a reserve function

  - by edA-qa mort-ora-y

  I use several maps and sets. The lack of contiguous memory, and high number of (de)allocations, is a performance bottleneck. I need a mainly STL-compatbile map and set class which can use a contiguous block of memory for internal objects (or multiple blocks). It also needs to have a reserve function so that I can preallocate for expected sizes. Before I write my own I'd like to check what is available first. Is there something in Boost which does this? Does somebody know of an available implementation elsewhere? Intrusive collection types are not usable here as the same objects need to exist in several collections. As far as I know STL memory pools are per-type, not per instance. These global pools are not efficient with respect to memory locality in mutli-cpu/core processing. Object pools don't work as the types will be shared between instance but their pool should not. In many cases a hash map may be an option in some cases.

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• How do I write test code to exercise a C# generic Pair<TKey, TValue> ?

  - by Scott Davies

  Hi, I am reading through Jon Skeet's "C# in Depth", first edition (which is a great book). I'm in section 3.3.3, page 84, "Implementing Generics". Generics always confuse me, so I wrote some code to exercise the sample. The code provided is: using System; using System.Collections.Generic; public sealed class Pair<TFirst, TSecond> : IEquatable<Pair<TFirst, TSecond>> { private readonly TFirst first; private readonly TSecond second; public Pair(TFirst first, TSecond second) { this.first = first; this.second = second; } ...property getters... public bool Equals(Pair<TFirst, TSecond> other) { if (other == null) { return false; } return EqualityComparer<TFirst>.Default.Equals(this.First, other.First) && EqualityComparer<TSecond>.Default.Equals(this.Second, other.Second); } My code is: class MyClass { public static void Main (string[] args) { // Create new pair. Pair thePair = new Pair(new String("1"), new String("1")); // Compare a new pair to previous pair by generating a second pair. if (thePair.Equals(new Pair(new string("1"), new string("1")))) System.Console.WriteLine("Equal"); else System.Console.WriteLine("Not equal"); } } The compiler complains: "Using the generic type 'ManningListing36.Paie' requires 2 type argument(s) CS0305" What am I doing wrong ? Thanks, Scott

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• C# reference collection for storing reference types

  - by ivo s

  I like to implement a collection (something like List<T>) which would hold all my objects that I have created in the entire life span of my application as if its an array of pointers in C++. The idea is that when my process starts I can use a central factory to create all objects and then periodically validate/invalidate their state. Basically I want to make sure that my process only deals with valid instances and I don't re-fetch information I already fetched from the database. So all my objects will basically be in one place - my collection. A cool thing I can do with this is avoid database calls to get data from the database if I already got it (even if I updated it after retrieval its still up-to-date if of course some other process didn't update it but that a different concern). I don't want to be calling new Customer("James Thomas"); again if I initted James Thomas already sometime in the past. Currently I will end up with multiple copies of the same object across the appdomain - some out of sync other in sync and even though I deal with this using timestamp field on the MSSQL server I'd like to keep only one copy per customer in my appdomain (if possible process would be better). I can't use regular collections like List or ArrayList for example because I cannot pass parameters by their real local reference to the their existing Add() methods where I'm creating them using ref so that's not to good I think. So how can this be implemented/can it be implemented at all ? A 'linked list' type of class with all methods working with ref & out params is what I'm thinking now but it may get ugly pretty quickly. Is there another way to implement such collection like RefList<T>.Add(ref T obj)? So bottom line is: I don't want re-create an object if I've already created it before during the entire application life unless I decide to re-create it explicitly (maybe its out-of-date or something so I have to fetch it again from the db). Is there alternatives maybe ?

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• java generics and the addAll method

  - by neesh

  What is the correct type of argument to the addAll(..) method in Java collections? If I do something like this: Collection<HashMap<String, Object[]>> addAll = new ArrayList<HashMap<String, Object[]>>(); // add some hashmaps to the list.. currentList.addAll(newElements); //currentList is of type: List<? extends Map<String, Object[]>> I understand I need to initialize both variables. However, I get a compilation error (from eclipse): Multiple markers at this line - The method addAll(Collection<? extends capture#1-of ? extends Map<String,Object[]>>) in the type List<capture#1-of ? extends Map<String,Object[]>> is not applicable for the arguments (List<capture#2-of ? extends Map<String,Object[]>>) - The method addAll(Collection<? extends capture#1-of ? extends Map<String,Object[]>>) in the type List<capture#1-of ? extends Map<String,Object[]>> is not applicable for the arguments (Collection<HashMap<String,Object[]>>) what am I doing wrong?

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• Validating collection elements in WPF

  - by Chris

  I would like to know how people are going about validating collections in WPF. Lets say for example that I have an observable collection of ViewModels that I am binding to the items source of a grid, and the user can add new rows to the grid and needs to fill them. First of all I need to validate on each row to ensure that required fields of each ViewModel are filled in. This is fine and simple to do for each row. However, the second level of validation is on the collection as a whole. For example i want to ensure that no two rows of the collection have the same identifier, or that no two rows have the same name. Im basically checking for duplicate properties within different rows. I also have more complex conditions where I must ensure that there is at least one item within the collection that has some property set. How do I get a validation rule that would allow me to check these rules, validating on the whole collection rather than the individual items. I also want to print any validation error above the datagrid so that the user can fix the problem and the message will update or disappear as the user fixes each different rule. Anyone have any experience of the proper way to do this? Thanks Chris

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