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  • Splitting lists inside list haskell

    - by user3713267
    Hi I need to split list by an argument in Haskell. I found function like this group :: Int -> [a] -> [[a]] group _ [] = [] group n l | n > 0 = (take n l) : (group n (drop n l)) | otherwise = error "Negative n" But what if lists that I want to divide are contained by another list? For example group 3 [[1,2,3,4,5,6],[2,4,6,8,10,12]] should return [[[1,2,3],[4,5,6]],[[2,4,6],[8,10,12]]] Is there any way to do that ?

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  • How to access a list in OCaml

    - by Erik
    I want to write a function that could check every item in a list is true or false. If at least one element is false, it will return true, so that: assert_eq "checkFalse [true; false; true]" (checkFalse [true; true; true]) false; assert_eq "checkFalse [false; false]" (checkFalse [false; true]) true; I am an absolute beginner in OCaml and I don't know how to approach this. I tried using a for loop, something like: let rec checkFalse (bools: bool list) : bool = for i = 0 to bools.length do if bools.length == false then false else... (I don't know how to continue) Then it said "Unbound record field...." I also tried using find like: if (find false bools != Not_found) then true else false But my ways did not work. I came from a Java background. Thank you very much!

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  • How to initialise a STL vector/list with a class without invoking the copy constructor

    - by Warpspace
    I have a C++ program that uses a std::list containing instances of a class. If I call e.g. myList.push_back(MyClass(variable)); it goes through the process of creating a temporary variable, and then immediately copies it to the vector, and afterwards deletes the temporary variable. This is not nearly as efficient as I want, and sucks when you need a deep copy. I would love to have the constructor of my class new something and not have to implement a copy constructor just to allocate my memory for the second time and waste runtime. I'd also rather not have to immediately find the class instance from the vector/list and then manually allocate the memory (or do something horrible like allocate the memory in the copy constructor itself). Is there any way around this (I'm not using Visual Studio BTW)?

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  • How to convert List<int> to string[]?

    - by George Edison
    I need an easy way to convert a List<int> to a string array. I have: var the_list = new List<int>(); the_list.Add(1); the_list.Add(2); the_list.Add(3); string[] the_array = new string[the_list.Count]; for(var i = 0 ; i < the_array.Count; ++i) the_array[i] = the_list[i].ToString(); ...which looks to be very ugly to me. Is there an easier way? Note: I'm looking for an easier way - not necessarily a faster way.

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  • C++: Comparing list of doubles with some invalid values (QNAN)

    - by J.M.
    Hello, i need to compare two std::list < double , but some doubles may be invalid numbers (QNAN). If any invalid numbers are list entries the compare process won't work, because a comparison of the same invalid value will always result in 'false'. What is the easiest and most elegant way to solve the problem? My idea was to create copies of both lists, iterate through them and remove invalid values and then compare the remaining lists. The lists will typically have 20-50 values in them. Is there a more resource friendly way to solve it?

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  • Android list all images available

    - by Javadid
    hi friends, I m making an application which requires me to list all the images available on the SD-Card of the phone. i tried querying the ContentResolver way i.e. Cursor image = getContentResolver().query(Images.Media.EXTERNAL_CONTENT_URI, new String[]{Images.Media._ID,Images.Media.DATA,Images.Media.DISPLAY_NAME}, null, null, null); but without any result. Is there any way i can get the list or if thats not possible then is there any possible intent (e.g. PICK) by which i can allow the user to select a file and then access the path of the file the user selected?? Helppppp guys...

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  • reverse a linked list?

    - by sil3nt
    Hi there, Im trying to reverse the order of the following linked list, I've done so, But the reversed list does not seem to print out. Where have I gone wrong? //reverse the linked list #include <iostream> using namespace std; struct node{ int number; node *next; }; node *A; void addNode(node *&listpointer, int num){ node *temp; temp = new node; temp->number = num; temp->next = listpointer; listpointer = temp; } void reverseNode(node *&listpointer){ node *temp,*current; current = listpointer; temp = new node; while (true){ if (current == NULL){ temp = NULL; break; } temp->number = current->number; current = current->next; temp = temp->next; } listpointer = temp; } int main(){ A = NULL; addNode(A,1); addNode(A,2); addNode(A,3); while (true){ if (A == NULL){break;} cout<< A->number << endl; A = A->next; } cout<< "****" << endl; reverseNode(A); while (true){ if (A == NULL){break;} cout<< A->number << endl; A = A->next; } cout<< "****"<< endl; return 0; }

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  • do.call(rbind, list) for uneven number of column

    - by h.l.m
    I have a list, with each element being a character vector, of differing lengths I would like to bind the data as rows, so that the column names 'line up' and if there is extra data then create column and if there is missing data then create NAs Below is a mock example of the data I am working with x <- list() x[[1]] <- letters[seq(2,20,by=2)] names(x[[1]]) <- LETTERS[c(1:length(x[[1]]))] x[[2]] <- letters[seq(3,20, by=3)] names(x[[2]]) <- LETTERS[seq(3,20, by=3)] x[[3]] <- letters[seq(4,20, by=4)] names(x[[3]]) <- LETTERS[seq(4,20, by=4)] The below line would normally be what I would do if I was sure that the format for each element was the same... do.call(rbind,x) I was hoping that someone had come up with a nice little solution that matches up the column names and fills in blanks with NAs whilst adding new columns if in the binding process new columns are found...

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  • Getting values from datagrid view column to list<>

    - by EvanRyan
    My main form in my application has a datagrid view that can have 1 to many user selected inputs. Column 8 of this grid is for the user to input "time in minutes." I have a separate class where I have built a timer that counts down from whatever time the user specifies down to 0. What I need is to create a series of alarms that go off as the timer counts down that are triggered by the user input values in column 8 of my datagrid. I think the best way to do this is to build a list< from the values in the datagrid. I for whatever reason can't quite figure out how to get the values from the datagrid in to a list< in my other class. Hopefully I explained in a way that makes sense.

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  • How to convert c++ std::list element to multimap iterator

    - by user63898
    Hello all, I have std::list<multimap<std::string,std::string>::iterator> > Now i have new element: multimap<std::string,std::string>::value_type aNewMmapValue("foo1","test") I want to avoid the need to set temp multimap and do insert to the new element just to get its iterator back so i could to push it back to the: std::list<multimap<std::string,std::string>::iterator> > can i somehow avoid this creation of the temp multimap. Thanks

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  • Show me some cool python list comprehensions

    - by christangrant
    One of the major strengths of python and a few other (functional) programming languages are the list comprehension. They allow programmers to write complex expressions in 1 line. They may be confusing at first but if one gets used to the syntax, it is much better than nested complicated for loops. With that said, please share with me some of the coolest uses of list comprehensions. (By cool, I just mean useful) It could be for some programming contest, or a production system. For example: To do the transpose of a matrix mat >>> mat = [ ... [1, 2, 3], ... [4, 5, 6], ... [7, 8, 9], ... ] >>> [[row[i] for row in mat] for i in [0, 1, 2]] [[1, 4, 7], [2, 5, 8], [3, 6, 9]] Please include a description of the expression and where it was used (if possible).

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  • How to bind a List<DateTime> to a DataGridView/ListBox .NET C#

    - by nat
    Hi there I have a List that I want to bind to a DataGridView in a windows forms app. however, I cannot for the life of me find the DataPropertyName I need to show what I want. I have had similar problems with binding this list to a listbox. what i really want is to show .ToString("dddd, dd MMMM yyyy HH:mm"), or certainly more than the standard 'date' part of the datetime - do i need to add a property of my own? public partial class DateTime{ public string myFormat{ get{return this.ToString("dddd dd MMM yyyy HH:mm");} } } or some such? thanks nat

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  • Generate all the ways to intersperse a list of lists, keeping each list in order.

    - by dreeves
    Given a list of lists like this [[1,2,3],[a,b,c,d],[x,y]] generate all permutations of the flattened list, [1,2,3,a,b,c,d,x,y], such that the elements of each sublist occur in the same order. For example, this one is okay [a,1,b,2,x,y,3,c,d] but this one is not [y,1,2,3,a,b,c,x,d] because y must occur after x, that being how x and y are ordered in the original sublist. I believe the number of such lists is determined by the multinomial coefficient. I.e., if there are k sublists, n_i is the length of the ith sublist, and n is the sum of the n_i's then the number of such permutations is n!/(n_i! * ... * n_k!). The question is how to generate those sublists. Pseudocode is great. An actual implementation in your language of choice is even better!

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  • Haskell, list of natural number

    - by Hellnar
    Hello, I am an absolute newbie in Haskell yet trying to understand how it works. I want to write my own lazy list of integers such as [1,2,3,4,5...]. For list of ones I have written ones = 1 : ones and when tried, works fine: *Main> take 10 ones [1,1,1,1,1,1,1,1,1,1] How can I do the same for increasing integers ? I have tried this but it indeed fails: int = 1 : head[ int + 1] And after that how can I make a method that multiplies two streams? such as: mulstream s1 s2 = head[s1] * head[s2] : mulstream [tail s1] [tail s2]

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  • XPath 1.0 to find if an element's value is in a list of values

    - by user364902
    Is there a way to construct an XPath that evaluates whether an element's value is in a predefined list of values? Something akin to this: /Location/Addr[State='TX or AL or MA'] Which would match nodes whith State elements for Texas, Alabama, or Massachusetts? I know that I can unpack the expression: /Location/Addr[State='TX] or /Location/Addr[State='AL'], etc... But this is a bit cumbersome since the xpaths are quite long, as is the list of values. My google-fu isn't turning up much on the issue...

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  • sort a list of objects based on runtime property

    - by jijo
    I have an arraylist of VOs. These objects have many properties and corresponding get/set methods. I want to sort this array list based on a property which I'll be getting in runtime. Let me explain in detail. My VO is like this public class Employee { String name; String id; private String getName() { return name; } private String getId() { return id; } } I will be getting a string ‘sort’ in runtime, which can be either ‘id’ of ‘name’. I want to sort the list based on the value of the string. I have tried to use comparator and reflection together, but no luck. I don’t want to use an if loop and create new comparator classes. Any other thoughts?

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  • Java - java.util.List problem

    - by Yatendra Goel
    I have a java.util.ArrayList<Item> and an Item object. Now, I want to obtain the number of times the Item is stored in the arraylist. I know that I can do arrayList.contains() check but it returns true, irrespective of whether it contains one or more Items. Q1. How can I find the number of time the Item is stored in the list? ================================================================================== Q2. Also, If the list contains more than one Item, then how can I determine the index of other Items because arrayList.indexOf(item) returns the index of only first Item every time?

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  • categorizing items in a list with python

    - by jtc99
    Just as a heads up, I'm really new to python. Currently I have a list of 110,000 donors in Excel. One of the pieces of information they give to us is their occupation. I would like to condense this list down to say 10 or 20 categories that I define. Normally I would just chug through this, going line by line, but since I have to do this for a years worth of data, I don't really have the time to do a line by line of 1,000,000+ rows. Is there anyway to define my 10 or 20 categories and then have python sort it out from there?

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  • list within a list

    - by atm atm
    I'm working on this problem, but I cannot figure out the second part. I tried using reverse list but it did not work out how I planned it. Given a list L (e.g. [1,2,3,4]), write a program that generates the following nested lists: L1 = [[1],[1,2],[1,2,3],[1,2,3,4]], L2 = [[4],[3,4],[2,3,4],[1,2,3,4]]. My code that I have so far: mylist=[,1,2,3,4] print("Orginal list L=",mylist) n=len(mylist) l1=[] l2=[] for x in range(1,n+1,1): l1.append(mylist[0:x]) print("L1=",l1) #prints final product of l1 mylist.reverse() #this is where i get messed up for x in range(1,n+1,1): l2.append(mylist[0:x]) print("L2=",l2)

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  • Iterators over a LInked List in a Game in Java

    - by Matthew
    I am using OpenGl in android and they have a callback method called draw that gets called with out my control. (As fast as the device can handle if I am not mistaken) I have a list of "GameObjects" that have a .draw method and a .update method. I have two different threads that handle each of those. So, the question is, can I declare two different iterators in two different methods in two different threads that iterate over the same Linked List? If so, do I simply declare ListIterator<GameObject> l = objets.listIterator() each time I want a new iterator and it won't interfere with other iterators?

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