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  • Haskell Add Function Return to List Until Certain Length

    - by kienjakenobi
    I want to write a function which takes a list and constructs a subset of that list of a certain length based on the output of a function. If I were simply interested in the first 50 elements of the sorted list xs, then I would use fst (splitAt 50 (sort xs)). However, the problem is that elements in my list rely on other elements in the same list. If I choose element p, then I MUST also choose elements q and r, even if they are not in the first 50 elements of my list. I am using a function finderFunc which takes an element a from the list xs and returns a list with the element a and all of its required elements. finderFunc works fine. Now, the challenge is to write a function which builds a list whose total length is 50 based on multiple outputs of finderFunc. Here is my attempt at this: finish :: [a] -> [a] -> [a] --This is the base case, which adds nothing to the final list finish [] fs = [] --The function is recursive, so the fs variable is necessary so that finish -- can forward the incomplete list to itself. finish ps fs -- If the final list fs is too small, add elements to it | length fs < 50 && length (fs ++ newrs) <= 50 = fs ++ finish newps newrs -- If the length is met, then add nothing to the list and quit | length fs >= 50 = finish [] fs -- These guard statements are currently lacking, not the main problem | otherwise = finish [] fs where --Sort the candidate list sortedps = sort ps --(finderFunc a) returns a list of type [a] containing a and all the -- elements which are required to go with it. This is the interesting -- bit. rs is also a subset of the candidate list ps. rs = finderFunc (head sortedps) --Remove those elements which are already in the final list, because -- there can be overlap newrs = filter (`notElem` fs) rs --Remove the elements we will add to the list from the new list -- of candidates newps = filter (`notElem` rs) ps I realize that the above if statements will, in some cases, not give me a list of exactly 50 elements. This is not the main problem, right now. The problem is that my function finish does not work at all as I would expect it to. Not only does it produce duplicate elements in the output list, but it sometimes goes far above the total number of elements I want to have in the list. The way this is written, I usually call it with an empty list, such as: finish xs [], so that the list it builds on starts as an empty list.

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  • This code appears to achieve the return of a null reference in C++

    - by Chuck
    Hi folks, My C++ knowledge is somewhat piecemeal. I was reworking some code at work. I changed a function to return a reference to a type. Inside, I look up an object based on an identifier passed in, then return a reference to the object if found. Of course I ran into the issue of what to return if I don't find the object, and in looking around the web, many people claim that returning a "null reference" in C++ is impossible. Based on this advice, I tried the trick of returning a success/fail boolean, and making the object reference an out parameter. However, I ran into the roadblock of needing to initialize the references I would pass as actual parameters, and of course there is no way to do this. I retreated to the usual approach of just returning a pointer. I asked a colleague about it. He uses the following trick quite often, which is accepted by both a recent version of the Sun compiler and by gcc: MyType& someFunc(int id) { // successful case here: // ... // fail case: return *static_cast<MyType*>(0); } // Use: ... MyType& mt = somefunc(myIdNum); if (&mt) // test for "null reference" { // whatever } ... I have been maintaining this code base for a while, but I find that I don't have as much time to look up the small details about the language as I would like. I've been digging through my reference book but the answer to this one eludes me. Now, I had a C++ course a few years ago, and therein we emphasized that in C++ everything is types, so I try to keep that in mind when thinking things through. Deconstructing the expression: "*static_cast(0);", it indeed seems to me that we take a literal zero, cast it to a pointer to MyType (which makes it a null pointer), and then apply the dereferencing operator in the context of assigning to a reference type (the return type), which should give me a reference to the same object pointed to by the pointer. This sure looks like returning a null reference to me. Any advice in explaining why this works (or why it shouldn't) would be greatly appreciated. Thanks, Chuck

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  • SQL Select for multiple where clause

    - by Tony
    Hi, I am trying to create SQL Select that returns counts of a certain field based on a field. So, here is what I am trying to do. Select count(distinct id) as TotalCount, -- this will be the total of id count(distinct id where type='A') as TotalA, -- this will be total when type='A' count(distinct id where type='B') as TotalB -- This will be total when type = 'B' from MyTable Basically, TotalCount = TotalA + TotalB. How can I achieve this in SQL Select Statement? Thanks.

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  • Bash Script (Cygwin) to grep a logfile for multiple phrases and output a new file for each phrase.

    - by Chris
    Each logfile is titled based on the date it was created in the format YYYY-MM-DD.txt. I need to search each file for five different keywords and output five files prepended with the specific keyword and then the original logfile name. Example: Test-YYYY-MM-DD.txt grep -i -w 'keyword1' YYYY-MM-DD.txt Keyword1-YYYY-MM-DD.txt If it's also possible to email each new file to a different person, that would be helpful as well.

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  • How do i generate hubernate models for java dotCMS plugins

    - by shuxer
    Hi I am trying to create a plugin for dotCMS. My plugin stores data in database. i defined hibernate mapping file and put in my plugin folder's conf dir and i have no idea how to hibernate generate models based my mapping definition. I am using hello world plugin's mapping file for mysql Any help or comment would be highly appreciated Thanks in advance

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  • Internet Explorer dont show a piece of my site

    - by Ramza
    Hi guys, i am creating a new site, based in a pre-existing web page The original site is http://oasisrio.intermediasp.com/ Its works great in Firefox, Chrome, and IE But the new one "oasisba.intermediasp.com" Dont show the right bar in IE, i check all that i can think about and i dont found the problem. Someone have any ideas why this is happening? PD: Sorry for my crapy english

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  • Python command line - add PYTHONPATH during module run

    - by orokusaki
    I want to run: python somescript.py somecommand But, when I run this I need PYTHONPATH to include a certain directory. I can't just add it to my environment variables because the directory I want to add changes based on what project I'm running. Is there a way to alter PYTHONPATH while running a script? Note: I don't even have a PYTHONPATH variable, so I don't need to worry about appending to it vs overriding it during running of this script.

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  • Open an external program in Qt with an attached file extension

    - by Phil
    I am making a qt application which allows the user to select a file and then upon clicking ok, start the associated program with the file already loaded. The program I want to start is java based, and I know how to use QProcess to get it to open, I don't know however how to add the file extension which the user is selecting. Any suggestions?

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  • Defining relationship in value objects using Hibernate

    - by kate
    Hi, We have three tables .We need to get data from these tables based upon particular conditions. Like if TableA.columv=TableB.columc=tableC.column then get data. We are using value objects to map Objects to relations. Question is how to maintain these relation ships in value objects. And how to retrieve data from it. We have one value object per table.

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  • MySQL Query to find consecutive available times of variable lenth

    - by Armaconn
    I have an events table that has user_id, date ('2013-10-01'), time ('04:15:00'), and status_id; What I am looking to find is a solution similar to http://stackoverflow.com/questions/2665574/find-consecutive-rows-calculate-duration but I need I need two additional components: 1) Take date into consideration, so 10/1/2013 at 11:00 PM - 10/2/2013 at 3:00AM. Feel free to just put in a fake date range (like '2013-10-01' to '2013-10-31') 2) Limit output to only include when there are 4+ consecutive times (each event is 15 minutes and I want it to display minimum blocks of an hour, but would also like to be able to switch this restriction to 1.5 hours or some other duration if possible). SUMMARY - Looking for a query that provides the start and end times for a set of events that have the same user_id, status_id, and are in a continuous series based on date and time. For which I can restrict results based on date range and minimum series duration. So the output should have: user_id, date_start, time_start, date_end, time_end, status_id, duration CREATE TABLE `events` ( `event_id` int(11) NOT NULL auto_increment COMMENT 'ID', `user_id` int(11) NOT NULL, `date` date NOT NULL, `time` time NOT NULL, `status_id` int(11) default NULL, PRIMARY KEY (`event_id`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 AUTO_INCREMENT=1568 ; INSERT INTO `events` VALUES(1, 101, '2013-08-14', '23:00:00', 2); INSERT INTO `events` VALUES(2, 101, '2013-08-14', '23:15:00', 2); INSERT INTO `events` VALUES(3, 101, '2013-08-14', '23:30:00', 2); INSERT INTO `events` VALUES(4, 101, '2013-08-14', '23:45:00', 2); INSERT INTO `events` VALUES(5, 101, '2013-08-15', '00:00:00', 2); INSERT INTO `events` VALUES(6, 101, '2013-08-15', '00:15:00', 1); INSERT INTO `events` VALUES(7, 500, '2013-08-14', '23:45:00', 1); INSERT INTO `events` VALUES(8, 500, '2013-08-15', '00:00:00', 1); INSERT INTO `events` VALUES(9, 500, '2013-08-15', '00:15:00', 2); INSERT INTO `events` VALUES(10, 500, '2013-08-15', '00:30:00', 2); INSERT INTO `events` VALUES(11, 500, '2013-08-15', '00:45:00', 1); Desired output row |user_id | date_start | time_start | date_end | time_end | status_id | duration 1 |101 |'2013-08-14'| '23:00:00' |'2013-08-15'|'00:15:00'| 2 | 5 2 |101 |'2013-08-15'| '00:00:15' |'2013-08-15'|'00:30:00'| 1 | 1 3 |500 |'2013-08-14'| '00:23:45' |'2013-08-15'|'00:15:00'| 1 | 2 4 |500 |'2013-08-15'| '00:00:15' |'2013-08-15'|'00:45:00'| 2 | 2 5 |500 |'2013-08-15'| '00:00:45' |'2013-08-15'|'01:00:00'| 2 | 1 *except that rows 2 and 5 wouldn't appear if duration had to be greater than 30 minutes Thanks for any help that you can provide! And please let me know if there is anything I can further clarify!!

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  • How does Python store lists internally?

    - by Mike Cooper
    How are lists in python stored internally? Is it an array? A linked list? Something else? Or does the interpreter guess at the right structure for each instance based on length, etc. If the question is implementation dependent, what about the classic CPython?

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  • PODS + WordPress + User Registration

    - by Sharath
    So I have PODS installed on my wordpress site that I am developing. I need to put up a user registration system such that once the user registers, he/she can be directed to POD pages that I have created. Can I just use the default registration system that comes with wordpress and redirect users based on a default role I assign to them? I basically don't want my potential users to view any part of the admin site. Any help is appreciated.

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  • Add data to a list box from a dropdown

    - by bachchan
    I have a listbox (listBox) and a dropdown list(dropDown). I want to be able to select an item from the dropDown and add them to the listBox. I have looked everywhere for this but all I ever see is adding data from a datasource instead of a dropdown. I want this to be dynamic so the listBox is populated based on the a user selected in the dropDown

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  • IN 'mytextfile.txt' syntax - access

    - by I__
    i would like to use this syntax to update a table in access based on data from a txtfile. fenton in his comments on this answer: http://stackoverflow.com/questions/2992168/read-text-file-line-by-line-and-insert-update-values-in-table/2992337#2992337 said that this is possible and i would like to see the exact syntax please

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  • Zend_Paginator / Doctrine 2

    - by Kevin
    I'm using Doctrine 2 with my Zend Framework application and a typical query result could yield a million (or more) search results. I want to use Zend_Paginator in line with this result set. However, I don't want to return all the results as an array and use the Array adapter as this would be inefficient, instead I would like to supply the paginator the total amount of rows then and array of results based on limit/offset amounts. Is this doable using the Array adapter or would I need to create my own pagination adapter?

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  • How does one go about writing a virtual MIDI interface?

    - by Alex
    I want to do some funky things with controlling MIDI streams, and I'd like to be able to pipe MIDI input into an application like Ableton or Reason. Presumably this involves some sort of driver level work? Ultimately I'd like to write my application in Python, so if there is some Python-based solution, I'd consider it. I'm perfectly fine with using C/C++, though, so that's not a problem.

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  • How do you put a UIWebView somewhere other than MainView.xib?

    - by Jack
    Hello, I've been trying to put a UIWebView into my app, which is tableview based. When the user selects a row, I want the new xib to load, but this one with a UIWebView on it. From all of the tutorials I've seen, you can only put a UIWebView on the MainView.xib. Can someone please tell me how to put a FUNCTIONING UIWebView somewhere other than the main view? Thanks in advance!!

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