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  • Efficient persistent storage for simple id to table of values map for java

    - by wds
    I need to store some data that follows the simple pattern of mapping an "id" to a full table (with multiple rows) of several columns (i.e. some integer values [u, v, w]). The size of one of these tables would be a couple of KB. Basically what I need is to store a persistent cache of some intermediary results. This could quite easily be implemented as simple sql, but there's a couple of problems, namely I need to compress the size of this structure on disk as much as possible. (because of amount of values I'm storing) Also, it's not transactional, I just need to write once and simply read the contents of the entire table, so a relational DB isn't actually a very good fit. I was wondering if anyone had any good suggestions? For some reason I can't seem to come up with something decent atm. Especially something with an API in java would be nice.

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  • querying larg text file containing JSON objects.

    - by Maciek Sawicki
    Hi, I have few Gigabytes text file in format: {"user_ip":"x.x.x.x", "action_type":"xxx", "action_data":{"some_key":"some_value"...},...} each entry is one line. First I would like to easily find entries for given ip. This part is easy because I can use grep for example. However even for this I would like to find better solution because I would like to get response as fast as possible. Next part is more complicated because I would like to find entries from selected ip and of selected type and with particular value of some_key in action_data. Probably I would have to convert this file to SQL db (probably SQLite, because it will be desktop APP), but I would ask if there are exists better solutions?

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  • Which data structure for List of objects + datagrid wiev

    - by Martin
    Hi, I have to develop a code which will store a list of objects, as example below 101, value 11, value 12, value 13 ...etc 102, value 21, value 22, value 23 ...etc 103, value 31, value 32, value 33 ...etc 104, value 41, value 42, value 43 ...etc Now, the difficulty is, that first column is an identifier, and whole table should always be sorted by it. Easy access to each element is required. Additionally, list should be easily updated, and extended by adding element at the end as well as in front and still keep being sorted by first column. Finally, I would like to be able to display values of the above in datagridview. What is most important is a performance of the implementation, as rows will be updated many times per second, and datagridview should be able to display all changes immediately. I was thinking about creating class for the values, and then a Dictionary but encountered a problem with displaying values in gridview. What would be the most optimal way of implementing the code? Thanks in advance Martin

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  • Transferring Data Between Server and Client (Mobile)

    - by Byron
    Scenario: Client (Mobile) - .Net CF 2.0, SQL CE 3.0 Server - .Net 2.0, SQL Server 2005, Web Service Client and Server database schemas differ. From server - only certain columns from certain tables need to be synced. From client - everything will need to be synced once client has made changes. Client will continually poll a web service to download and upload data. A framework will be developed to package and unpackage data, used by both client and server. How would you develop the packaging and unpackaging? Use datasets, serialise strongly typed objects? All suggestions welcome. Thanks

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  • How to implement a simple queue properly?

    - by Stephen Hsu
    The current Go library doesn't provide the queue container. To implement a simple queue, I use circle array as the underlying data structure. It follows algorithms mentioned in TAOCP: Insert Y into queue X: X[R]<-Y; R<-(R+1)%M; if R=F then OVERFLOW. Delete Y from queue X: if F=R then UNDERFLOW; Y<-X[F]; F<-(F+1) % M. F: Front, R: Rear, M: Array length. Following is the code: package main import ( "fmt" ) type Queue struct { len int head, tail int q []int } func New(n int) *Queue { return &Queue{n, 0, 0, make([]int, n)} } func (p *Queue) Enqueue(x int) bool { p.q[p.tail] = x p.tail = (p.tail + 1) % p.len return p.head != p.tail } func (p *Queue) Dequeue() (int, bool) { if p.head == p.tail { return 0, false } x := p.q[p.head] p.head = (p.head + 1) % p.len return x, true } func main() { q := New(10) for i := 1; i < 13; i++ { fmt.Println(i, q.Enqueue(i)) } fmt.Println() for i := 1; i < 13; i++ { fmt.Println(q.Dequeue()) } } But the output is obviously wrong: 1 true 2 true 3 true 4 true 5 true 6 true 7 true 8 true 9 true 10 false 11 true 12 true 11 true 12 true 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false 0 false I think I need one more field to make the code work properly. What do you suggest?

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  • Managing changes in memory-based data format

    - by kamziro
    So I've been using a compact data type in c++, and saving from memory or loading from the file involves just copying the bits of memory in and out. However, the obvious drawback of this is that if you need to add/remove elements on the data, it becomes kind of messy. There's also problems with versioning, suppose you distribute a program which uses version A of the data, and then the next day you make version B of it, and then later on version C. I suppose this can be solved by using something like xml or json. But suppose you can't do that for technical reasons. What is the best way to do this, apart from having to make different if cases etc (which would be pretty ugly, I'd imagine)

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  • advanced python autovivification

    - by Zhang18
    This question is about implementing the full PERL autovivification in python. I know similary questions were asked before and so far the best answre is http://stackoverflow.com/questions/635483/what-is-the-best-way-to-implement-nested-dictionaries-in-python/652284#652284. However, I'm looking to do this: a['x']['y'].append('z') without declaring a['x']['y'] = [] first, or rather, not declaring a['x'] = {} either. I know dict and list classes sorta don't mix so this is hard, but I'm interested in seeing if someone has an ingenius solution probably involving creating an inherited class from dict but defined a new append method on it? I also know this might throw off some python purists who will ask me to stick with Perl. But even just for a challenge, I'd like to see something. thx!

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  • Interview question: How do I detect a loop in this linked list?

    - by jjujuma
    Say you have a linked list structure in Java. It's made up of Nodes: class Node { Node next; // some user data } and each Node points to the next node, except for the last Node, which has null for next. Say there is a possibility that the list can contain a loop - i.e. the final Node, instead of having a null, has a reference to one of the nodes in the list which came before it. What's the best way of writing boolean hasLoop(Node first) which would return true if the given Node is the first of a list with a loop, and false otherwise? How could you write so that it takes a constant amount of space and a reasonable amount of time? Here's a picture of what a list with a loop looks like: Node->Node->Node->Node->Node->Node--\ \ | ----------------

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  • Revisions: algorithm and data structure

    - by SODA
    Hi, I need ideas for structuring and processing data with revisions. For example, I have a database of objects (e.g. cars). Each object has a number of properties, which can be arbitrary, so there's no a set schema to describe these objects. These objects are probably saved as key-value pairs. Now I need to change property of an object. I don't want to completely rewrite it - I want to be able to go back and see history of changes to these properties, that's why I want to add new property and keep the old one (so I guess a timestamp would do the job of telling which property is the latest). At the same time I want to be able to get info about any object in a snap, with only latest versions of each of the properties. Any ideas what would be the best approach? At least please point me in the right direction. Thanks!

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  • How do you store sets in Cassandra?

    - by Ben W
    I'd like to convert this JSON to a data model in Cassandra, where each of the arrays is a set with no duplicates: var data = { "data1": { "100": [1, 2, 3], "200": [3, 4] }, "data2": { "k1", [1], "k2", [4, 5] } } I'd like to query like this: data["data1"]["100"] to retrieve the sets. Anyone know how you might model this in Cassandra? (The only thing I came up with was columns whose name was a set value and the value of the column was an empty string, but that felt wrong.) It's not OK to serialize the sets as JSON or some other string, which would make this much easier. Also, I should note that it's OK to split data1 and data2 into separate ColumnFamilies, it's not necessary that they're keys in the same one.

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  • Why can't RB-Tree be a list?

    - by Alex
    Hey everyone. I have a problem with the rb-trees. according to wikipedia, rb-tree needs to follow the following: A node is either red or black. The root is black. (This rule is used in some definitions and not others. Since the root can always be changed from red to black but not necessarily vice-versa this rule has little effect on analysis.) All leaves are black. Both children of every red node are black. Every simple path from a given node to any of its descendant leaves contains the same number of black nodes. As we know, an rb-tree needs to be balanced and has the height of O(log(n)). But, if we insert an increasing series of numbers (1,2,3,4,5...) and theoretically we will get a tree that will look like a list and will have the height of O(n) with all its nodes black, which doesn't contradict the rb-tree properties mentioned above. So, where am I wrong?? thanks.

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  • Modifying C# dictionary value

    - by minjang
    I'm a C++ expert, but not at all for C#. I created a Dictionary<string, STATS>, where STATS is a simple struct. Once I built the dictionary with initial string and STATS pairs, I want to modify the dictionary's STATS value. In C++, it's very clear: Dictionary<string, STATS*> benchmarks; Initialize it... STATS* stats = benchmarks[item.Key]; // Touch stats directly However, I tried like this in C#: Dictionary<string, STATS> benchmarks = new Dictionary<string, STATS>(); // Initialize benchmarks with a bunch of STATS foreach (var item in _data) benchmarks.Add(item.app_name, item); foreach (KeyValuePair<string, STATS> item in benchmarks) { // I want to modify STATS value inside of benchmarks dictionary. STATS stat_item = benchmarks[item.Key]; ParseOutputFile("foo", ref stat_item); // But, not modified in benchmarks... stat_item is just a copy. } This is a really novice problem, but wasn't easy to find an answer. EDIT: I also tried like the following: STATS stat_item = benchmarks[item.Key]; ParseOutputFile(file_name, ref stat_item); benchmarks[item.Key] = stat_item; However, I got the exception since such action invalidates Dictionary: Unhandled Exception: System.InvalidOperationException: Collection was modified; enumeration operation may not execute. at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource) at System.Collections.Generic.Dictionary`2.Enumerator.MoveNext() at helper.Program.Main(String[] args) in D:\dev\\helper\Program.cs:line 75

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  • How does one implement storage/retrieval of smart-search/mailbox features?

    - by humble_coder
    Hi All, I have a question regarding implementation of smart-search features. For example, consider something like "smart mailboxes" in various email applications. Let's assume you have your data (emails) stored in a database and, depending on the field for which the query will be created, you present different options to the end user. At the moment let's assume the Subject, Verb, Object approach… For instance, say you have the following: SUBJECTs: message, to_address, from_address, subject, date_received VERBs: contains, does_not_contain, is_equal_to, greater_than, less_than OBJECTs: ??????? Now, in case it isn't clear, I want a table structure (although I'm not opposed to an external XMLesque file of some sort) to store (and later retrieve/present) my criteria for smart searches/mailboxes for later use. As an example, using SVO I could easily store then reconstruct a query for "date between two dates" -- simply use "date greater than" AND "date less than". However, what if, in the same smart search, I wanted a "between" OR'ed with another criterion? You can see that it might get out of hand -- not necessarily in the query creation (as that is rather simplistic), but in the option presentation and storage mechanism. Perhaps I need to think more on a more granular level. Perhaps I need to simply allow the user to select AND or OR for each entry independently instead of making it an ALL OR NOTHING type smart search (i.e. instead of MATCH ALL or MATCH ANY, I need to simply allow them to select -- I just don't want it to turn into a Hydra). Any input would be most appreciated. My apologies if the question is a bit incoherent. It is late, and I my brain is toast. Best.

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  • How good is the memory mapped Circular Buffer on Wikipedia?

    - by abroun
    I'm trying to implement a circular buffer in C, and have come across this example on Wikipedia. It looks as if it would provide a really nice interface for anyone reading from the buffer, as reads which wrap around from the end to the beginning of the buffer are handled automatically. So all reads are contiguous. However, I'm a bit unsure about using it straight away as I don't really have much experience with memory mapping or virtual memory and I'm not sure that I fully understand what it's doing. What I think I understand is that it's mapping a shared memory file the size of the buffer into memory twice. Then, whenever data is written into the buffer it appears in memory in 2 places at once. This allows all reads to be contiguous. What would be really great is if someone with more experience of POSIX memory mapping could have a quick look at the code and tell me if the underlying mechanism used is really that efficient. Am I right in thinking for example that the file in /dev/shm used for the shared memory always stays in RAM or could it get written to the hard drive (performance hit) at some point? Are there any gotchas I should be aware of? As it stands, I'm probably going to use a simpler method for my current project, but it'd be good to understand this to have it in my toolbox for the future. Thanks in advance for your time.

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  • Binary search in rotated sorted list

    - by Algorist
    I am having a sorted list which is rotated and I would like to do a binary search on that list to find the minimum element. Lets suppose initial list is {1,2,3,4,5,6,7,8} rotated list can be like {5,6,7,8,1,2,3,4} Normal binary search doesn't work in this case. Any idea how to do this.

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  • Huge Graph Structure

    - by Harph
    I'm developing an application in which I need a structure for represent a huge graph (between 1000000 and 6000000 nodes and 100 or 600 edges) in memory. The edges representation will contain some attribute of the relation. I have tried a memory map representation, arrays, dictionaries and string for represent that structure in memory, but this always crash because the memory limit. I would to get an advice of how can I represent this, or something similar. By the way, I'm using python.

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  • PHP: How to automate building a 100 <UL>/<LI> menuitems, while keeping the Menu Structure File Flat / Simply Managable?

    - by Sam
    Above: current "stupid" menu. (entire ul/li menu for javascript menu system) + (some li lines as page-specific submenu) Hi folks! With passion for automation and elegancy, but limited knowledge/knowhow, im stuck with "my hands in my hair" as we Dutch say, for my current menu system works perfectly, but is a pain in the a*s to update! So, i would appreciate it greatly, if you can suggest how to automate this in php: how to let the php generate the html menu code basing on a flat menu input file with TABS indented. OLD SITUATION <ul> <!-- about 100 of these <li>....</li> lines --> <li><a href="carrot.php"><p class="mnu" style="background-position:0 -820px"><? echo __("carrot juice") ?></p></a></li> <!-- lots of data, with only little bit thats really the menu itself--> </ul a javascript file reads a ul/li structure as input to build menu of format in that ul/li, the items with a hyperlink and sprite-bg position represent webpages, (inside LI) while items without hyperlink and sprite-bg are just headers of that menusection, (inside H6) to highlight the current page in the menu, the javascript menumaker uses an id number. this number corresponds to the consequtive li that is a webpage, skips h6 headers correctly. these h6 headers are only there for when importing sections of the same menu as submenu. non-li headers are not shown in menu, nore counted by the javascript menu for their ID. to know which page should be shown, i have to count from ID 0, the li items till finding the current webpage in the li structure and then manually put it in each webpage! BUT: changing an item in li order, means stupidly re-counting their entire li again! each webpage has an icon (= sprite bg-position numer), which is also used in the webpage. INTENDED RESULT I dream of, once setting what the current webpage is (e.g carrot.php) the menu system automatically "finds" and "counts" the li's and returns the id nr (for proper highlight of main menu); generates the entire menu html, and depending on which headings are set for submenu, (e.g. meals, drinks) generates those submenu (entire section below each given header); ginally adds h5 highlight inside the li of that submenu item. For the menu, i wish an easily readable, simple plain txt menu that is indented with tabs, (each tab is one depth for example) and further tabs follow for url and sprite position of icon. MY DREAM MENU-MANAGEMENT FILE |>TAB SEPARATED/INDENTED FLATMENU FILE |MUST BE CALCULATED BY PHP: |>MENUTEXT============URL=============SPRITE=====|ID===TAG================== |>about "#" -520 |00 li |> INFORMATION |—— h6 |> physical state "physical.php" -920 |01 li |> mental health "mental.php" -10 |02 li |> |>apetite "#" -1290 |03 li |> meals "#" -600 |04 li |> COLD MEAL |—— h6 |> egg salade "salad.php" -1040 |05 li |> salmon fish "salmon.php" -540 |06 li |> HOT MEAL |—— h6 |> spare ribs "spareribs.php" -120 |07 li |> di macaroni "macaroni.php" -870 |08 li |> |> drinks "#" -230 |09 li |> JUCY DRINK |—— h6 |> carrot juice "carrot.php" -820 |10 li |> mango hive "mango.php" -270 |11 li DESIRED CHRONOLOGY php outputs the entire ul/li html so the javascript can show the menu: webpage items go inside li tags, and header items go inside h6 tags, e.g. <h6>JUCY DRINK</h6> Each website page has a url filename [eg: salad.php]. Based on this given fact, the php menu generator detects the pagename, gives the IDnr of the position of that page according to the li-item nr and sets variable for javascript to highlight current menu item. the menu items below the specified headers are loaded as submenu in which the current page.php is wrapped inside h5 to highlight current page in submenu: e.g. (<li><h5><a href="carrot.php"><p>..etc..</p></h5></li> Question Which methods / steps / (chronological)ways are there for doing this? I am no good in php programming, but am learning it so please dont write any code without a line of comment why I should use that method etc. Where do I start? If I am unclear in my question, please ask. Thanks. Much appreciated!! Concrete Task List from the provided Comments/Answers, sofar: (RobertB) First, get some PHP code working that can read through a tab-delimited file and put the data into an appropriate data structure. NOW WORKING AT THIS

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  • How to Create Own HashMap in Java?

    - by Taranfx
    I know about hashing algorithm and hashCode() to convert "key" into an equivalent integer (using some mathematically random expression) that is then compressed and stored into buckets. But can someone point me to an implementation or at least data structure that should be used as baseline? I haven't found it anywhere on the web.

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  • AutoComplete implementation - Interview Question

    - by user181218
    Hi, Say you have a DB table with two cols: SearchPhrase(String) | Popularity(Int). You need to initialize a DS so that you could use it to implement an autocomplete feature (like google suggest) comfortably. The requirement: Once the data from the db is processed into the data structure, when you type a letter you get the 10 most popular searchphrases from the db starting with that letter,then when you type the next one you get the 10 .... with these two letters and so on. The question only concerns planning the ds and pseudocoding Insert,Search etc. Note: YOU CANNOT USE TRIE DS. Any ideas?

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  • When to use LinkedList<> over ArrayList<>?

    - by sdellysse
    I've always been one to simply use List<String> names = new ArrayList<String>(); I use the interface as the type name for portability, so that when I ask questions such as these I can rework my code. When should LinkedList should be used over ArrayList and vice-versa?

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  • Skip Lists -- ever used them?

    - by Head Geek
    I'm wondering whether anyone here has ever used a skip list. It looks to have roughly the same advantages as a balanced binary tree, but is simpler to implement. If you have, did you write your own, or use a pre-written library (and if so, what was its name)?

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  • Java Data Structure

    - by Joe
    Hi there, I'm looking for a data structure that will act like a Queue so that I can hava First In First Out behaviour, but ideally I would also be able to see if an element exists in that Queue in constant time as you can do with a HashMap, rather than the linear time that you get with a LinkedList. I thought a LinkedHashMap might do the job, but although I could make an iterator and just take and then remove the first element of the iteration to produce a sort of poll() method, I'm wondering if there is a better way. Many thanks in advance

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