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• Find top N elements in a Multiset from Google Collections?

  - by dfrankow

  A Google Collections Multiset is a set of elements each of which has a count (i.e. may be present multiple times). I can't tell you how many times I want to do the following Make a histogram (exactly Multiset) Get the top N values from the histogram Examples: top 10 URLs, top 10 tags, ... What is the canonical way to do #2 given a Multiset? Here is a blog post about it, but that code is not quite what I want. First, it returns everything, not just top N. Second, it copies (is it possible to avoid a copy?). Third, I usually want a deterministic sort, i.e. tiebreak if counts are equal.

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• Is it possible to apply inheritance to a Singleton class?

  - by Bragaadeesh

  Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as protected thinking that child's constructor also has be protected. But I was wrong the child can have a modifier either equal to or higher than that. So, I asked him to give a real world example on such a case. He was not able to give me one and said that I cant ask questions and wanted me to tell whether this scenario is possible or not. I went kind of blank. My question here is, Is this possible? Even if its possible, what is the use of it? What real world scenario would demand such a use. Thanks

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• Container for database-like searches

  - by Milan Babuškov

  I'm looking for some STL, boost, or similar container to use the same way indexes are used in databases to search for record using a query like this: select * from table1 where field1 starting with 'X'; or select * from table1 where field1 like 'X%'; I thought about using std::map, but I cannot because I need to search for fields that "start with" some text, and not those that are "equal to". I could create a sorted vector or list and use binary search (breaking the set in 2 in each step by reading the element in the middle and seeing if it's more or less than 'X'), but I wonder if there is some ready-made container I could use without reinventing the wheel?

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• 128bit hash comparison with SSE

  - by fokenrute

  Hi, In my current project, I have to compare 128bit values (actually md5 hashes) and I thought it would be possible to accelerate the comparison by using SSE instructions. My problem is that I can't manage to find good documentation on SSE instructions; I'm searching for a 128bit integer comparison instruction that let me know if one hash is larger, smaller or equal to another. Does such an instruction exists? PS: The targeted machines are x86_64 servers with SSE2 instructions; I'm also interested in a NEON instruction for the same job.

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• How can I find out how many rows of a matrix satisfy a rather complicated criterion (in R)?

  - by Brani

  As an example, here is a way to get a matrix of all possible outcomes of rolling 4 (fair) dice. z <- as.matrix(expand.grid(c(1:6),c(1:6),c(1:6),c(1:6))) As you may already have understood, I'm trying to work out a question that was closed, though, in my opinion, it's a challenging one. I used counting techniques to solve it (I mean by hand) and I finaly arrived to a number of outcomes, with a sum of subset being 5, equal to 1083 out of 1296. That result is consistent with the answers provided to that question, before it was closed. I was wondering how could that subset of outcomes (say z1, where dim(z1) = [1083,4] ) be generated using R. Do you have any ideas? Thank you.

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• Ambiguous Evaluation of Lambda Expression on Array

  - by Joe

  I would like to use a lambda that adds one to x if x is equal to zero. I have tried the following expressions: t = map(lambda x: x+1 if x==0 else x, numpy.array) t = map(lambda x: x==0 and x+1 or x, numpy.array) t = numpy.apply_along_axis(lambda x: x+1 if x==0 else x, 0, numpy.array) Each of these expressions returns the following error: ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() My understanding of map() and numpy.apply_along_axis() was that it would take some function and apply it to each value of an array. From the error it seems that the the lambda is being evaluated as x=array, not some value in array. What am I doing wrong? I know that I could write a function to accomplish this but I want to become more familiar with the functional programming aspects of python.

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• Side effects of reordering columns in PostgreSQL

  - by Summer

  I sometimes re-order the columns in my Postgres DB. Since Postgres can only add columns at the end of tables, I end up re-ordering by adding new columns at the end of the table, setting them equal to existing columns, and then dropping the original columns. My question is: what does PostgreSQL do with the memory that's freed by dropped columns? Does it automatically re-use the memory, so a single record consumes the same amount of space as it did beforehand? But that would require a re-write of the whole table, so to avoid that, does it just keep a bunch of blank space around in each record? Thanks! ~S

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• Php getting too many connections error from MySQL

  - by uzioriluzan

  Hello everyone, I am using MySQL and PHP with 2 application servers and 1 database server. With the increase of the number of users (around 1000 by now), I'm getting the following error : SQLSTATE[08004] [1040] Too many connections The parameter "max_connections" is set to "1000" in my.cnf and "mysql.max_persistent" is set to -1 in php.ini. There are at most 1500 apache processes running at a time since the "MaxClients" apache parameter is equal to 750 and we have 2 application servers. Should I raise the "max_connections" to 1500 as indicated in here? Or should I set "mysql.max_persistent" to 750 (we use PDO with persistent connections for performance reasons since the database server is not the same as the application servers)? Or should I try something else? Thanks in advance!

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• Distance between numpy arrays, columnwise

  - by Jaapsneep

  I have 2 arrays in 2D, where the column vectors are feature vectors. One array is of size F x A, the other of F x B, where A << B. As an example, for A = 2 and F = 3 (B can be anything): arr1 = np.array( [[1, 4], [2, 5], [3, 6]] ) arr2 = np.array( [[1, 4, 7, 10, ..], [2, 5, 8, 11, ..], [3, 6, 9, 12, ..]] ) I want to calculate the distance between arr1 and a fragment of arr2 that is of equal size (in this case, 3x2), for each possible fragment of arr2. The column vectors are independent of each other, so I believe I should calculate the distance between each column vector in arr1 and a collection of column vectors ranging from i to i + A from arr2 and take the sum of these distances (not sure though). Does numpy offer an efficient way of doing this, or will I have to take slices from the second array and, using another loop, calculate the distance between each column vector in arr1 and the corresponding column vector in the slice?

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• heirarchial data from self referencing table in tree form

  - by Beta033

  Ii looks like this has been asked and answered in all the simple cases, excluding the one that i'm having trouble with. I've tried using a recursive CTE to generate this, however maybe a cursor would be better? or maybe a set of recursive functions will do the trick? Can this be done in a cte? consider the following table PrimaryKey ParentKey 1 NULL 2 1 3 6 4 7 5 2 6 1 7 NULL should yield PK 1 -2 --5 -6 --3 7 -4 where the number of - marks equal the depth, my primary difficulty is the ordering.

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• Join with ADO.NET Linq to Entity in C#

  - by aladdin

  Hello I'm try to migrate a system to ADO.NET Entity I have 3 table A => (Id, Name, ...) B => (Id, Domain, ...) c => (IdA, IdB) VS.NET generate 2 entity A and B and both have reference to the other table but this reference is a collection. I need make a join between tables. from a in A join b in B on a.? equal b.? where condition select new { Name = a.Name, Domain = b.Domain }; I cant do that follow the reference in entity bu when the problem grows can be a problem. Any Help?

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• How it is better to organise a large database of addresses?

  - by shurik2533

  How it is better to organise a large database of addresses? It is need to create mysql database of addresses. How it is better for organising? I have two variants: 1) cuontries id|name 1 |Russia cities id|name 1 |Moscow 2 |Saratov villages id|name streets id|name 1 |Lenin st. places id|name |country_id|city_id|village_id|street_id|building_number|office|flat_number|room_number 1 |somebuilding |1 |1 |NULL |1 |31 |12a |NULL |NULL For simplification I use not all making addresses. If any part does not participate in the address it is equal NULL 2) addressElements id|name 1 |country 2 |city 3 |village 4 |street 5 |office 6 |flat_number 7 |room_number addressValues id|addressElement_id|value 1 |1 |Russia 2 |2 |Saratov 3 |2 |Moscow 4 |3 |Prostokvashino 5 |4 |Lenin st. places id| name 1 | somebuilding places_has_addressValues place_id|addressValue_id 1 |1 1 |3 1 |5 UPD. I have decided to make as follows

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• Help with Regex statement in Ruby

  - by user336777

  I have a string called 'raw'. I am trying to parse it in ruby in the following way: raw = "HbA1C ranging 8.0—10.0%" raw.scan /\d*.?\d+[ ](-+|\342\200\224)[ ]\d*.?\d+/ The output from the above is []. I think it should be: ["8.0—10.0"]. Does anyone have any insight into what is wrong with the above regex statement? Note: \342\200\224 is equal to '—'. The piece that is not working is: (-+|\342\200\224) I think it should be equivalent to saying, match on 1 or more '-' OR match on the string \342\200\224. Any help would be greatly appreciated it!

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• xUnit false positive when comparing null terminated strings

  - by mr.b

  I've come across odd behavior when comparing strings. First assert passes, but I don't think it should.. Second assert fails, as expected... [Fact] public void StringTest() { string testString_1 = "My name is Erl. I am a program\0"; string testString_2 = "My name is Erl. I am a program"; Assert.Equal<string>(testString_1, testString_2); Assert.True(testString_1.Equals(testString_2)); } Any ideas?

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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• MySQL Join issue

  - by mouthpiec

  Hi, I have the following tables: --table sportactivity-- sport_activity_id, home_team_fk, away_team_fk, competition_id_fk, date, time (tuple example) - 1, 33, 41, 5, 2010-04-14, 05:40:00 --table teams-- team_id, team_name (tuple example) - 1, Algeria Now I have the following SQL statment that I use to extract Team A vs Team B SELECT sport_activity_id, T1.team_name AS TeamA, T2.team_name AS TeamB, DATE_FORMAT( DATE, '%d/%m/%Y' ) AS DATE, DATE_FORMAT( TIME, '%H:%i' ) AS TIME FROM sportactivity JOIN teams T1 ON home_team_fk = T1.team_id JOIN teams T2 ON ( away_team_fk = T2.team_id OR away_team_fk = '0' ) WHERE DATE( DATE ) >= CURDATE( ) ORDER BY DATE( DATE ) My problem is that when team B is empty, I am having irrelevant information .... it seems that it is returning all the combinations. I need a query that when team B is equal to 0, (this can occur in my scenario) I get only Team A - Team B (as 0) once.

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• how many color combinations in a 24 bit image

  - by numerical25

  I am reading a book and I am not sure if its a mistake or I am misunderstanding the quote. It reads... Nowadays every PC you can buy has hardware that can render images with at least 16.7 million individual colors. Rather than have an array with thousands of color entries, the images instead contain explicit color values for each pixel. A 24-bit display, of course, uses 24 bits, or 3 bytes per pixel, for color information. This gives 1 byte, or 256 distinct values each, for red, green, and blue. This is generally called true color, because 256^3 (16.7 million) He says 1 byte is equal to 256 distinct values. 1 byte = 8 bits. 8^2 bits = 64 distinct colors right ?? It's not adding up right to me. I know it might be something simple to understand, but I don't understand.

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• how many color combinations in a 24 bit image

  - by numerical25

  I am reading a book and I am not sure if its a mistake or I am misunderstanding the quote. It reads... Nowadays every PC you can buy has hardware that can render images with at least 16.7 million individual colors. Rather than have an array with thousands of color entries, the images instead contain explicit color values for each pixel. A 24-bit display, of course, uses 24 bits, or 3 bytes per pixel, for color information. This gives 1 byte, or 256 distinct values each, for red, green, and blue. This is generally called true color, because 256^3 (16.7 million) He says 1 byte is equal to 256 distinct values. 1 byte = 8 bits. 8^2 bits = 64 combinations of colors right ?? It's not adding up right to me. I know it might be something simple to understand, but I don't understand.

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• Get the affinity of a SQLite column on Android

  - by Neil Traft

  The SQLite C library has a method, sqlite3_column_decltype(). But I cannot find any place where the Android SQLite API makes this method available. Is there any way to get the declared type of a column without running any SQL (i.e. can I avoid using PRAGMA table_info)? I could have used AbstractWindowedCursor.isBlob(), but it says that it will also return true if the field is NULL. I need something that will guarantee me a value equal to the column's declared type.

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• ASP.Net mysterious behaviour

  - by kalan

  Does anyone have any idea why this works (expression in the if-clause) if (!(childNode.Roles != null && !Helper.HasEqualElements((string[])childNode.Roles, System.Web.Security.Roles.GetRolesForUser()))) AddNode(childNode, parentNode); And this doesn't if (childNode.Roles == null || Helper.HasEqualElements((string[])childNode.Roles, System.Web.Security.Roles.GetRolesForUser())) AddNode(childNode, parentNode); The problem is that the second if-clause sometimes doesn't work. Though it always works in debug mode, but it sometimes fails while running. And the strange thing is that these two pieces of code seems absolutely equal for me.

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• Why is visual studio not aware that an integer's value is changing? (debugging)

  - by incrediman

  I have a few simple lines of code (below). [bp] indicates a breakpoint. for(int i=0;i<300;i++){} int i=0; cout<<i; [bp] for (i=0;i<200;i++){} When I debug this in visual studio, it tells me that i is equal to 300 on the breakpoint. Annoyingly, 0 is printed to the console. Is there any way to make it realize that two variables in different scopes can actually have the same name? I also want to add some code to the second loop and then debug it - but when I try to do that, i is consistently shown as 300. Very annoying.

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• Plotting a cumulative graph of python datetimes

  - by ventolin

  Say I have a list of datetimes, and we know each datetime to be the recorded time of an event happening. Is it possible in matplotlib to graph the frequency of this event occuring over time, showing this data in a cumulative graph (so that each point is greater or equal to all of the points that went before it), without preprocessing this list? (e.g. passing datetime objects directly to some wonderful matplotlib function) Or do I need to turn this list of datetimes into a list of dictionary items, such as: {"year": 1998, "month": 12, "date": 15, "events": 92} and then generate a graph from this list? Sorry if this seems like a silly question - I'm not all too familiar with matplotlib, and would like to save myself the effort of doing this the latter way if matplotlib can already deal with datetime objects itself.

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• 3 fixed Columns (header and footer) using DIVs, NO Absolute DIVs, IE friendly, ALL columns stretch e

  - by Phillip Schein

  Left to right, Col1 id 560px wide with 10 px padding, middle column, 250px wide with 5px padding and Col3 (siderbar) is 200px wide with 3px padding. Background coloR, no matter text length in any column should stretch vertically equal. No javascript (jQuery workarounds) to make it work. It needs to be pure Semantic Markup with CSS. Each Column should have a nested column of color were content will go. Column 1 should be SEO prominant which means the highest nested column for Google and other Search Engines to crawl. I have used 'The Holy Grail" layout, articles at "A List Apart" and these solution are so convoluted that they push the main columns left and than the nested columns push them with padding back right. This is crazy! I try to adjust these examples, but they're not editable by just adjusting a width in the CSS or the padding, etc. Can you please help me?

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• Specific Strings And NSScanner

  - by Garry

  I need to determine whether a string (sourceString) contains another string (queryString) and if it does, at what offset. I'm guessing that NSScanner might do the trick but I don't fully understand the documentation. Let's say sourceString = @"What's the weather in London today?" If I set queryString to equal @"What's the weather", I'd like a method that would determine that, in this case, YES (sourceString does contain queryString) and the offset is 0 (i.e. at the start of sourceString). Any suggestions?

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• Why only the constant expression can be used as case expression in Switch statement?

  - by sinec

  Hi, what is bothering me is that I can't found an info regarding the question from the title. I found that assembly form the Switch-case statement is compiled into bunch of (MS VC 2008 compiler) cmp and je calls: 0041250C mov eax,dword ptr [i] 0041250F mov dword ptr [ebp-100h],eax 00412515 cmp dword ptr [ebp-100h],1 0041251C je wmain+52h (412532h) 0041251E cmp dword ptr [ebp-100h],2 00412525 je wmain+5Bh (41253Bh) 00412527 cmp dword ptr [ebp-100h],3 0041252E je wmain+64h (412544h) 00412530 jmp wmain+6Bh (41254Bh) where for above code will in case that if condition (i) is equal to 2, jump to address 41253Bh and do execution form there (at 41253Bh starts the code for 'case 2:' block) What I don't understand is why in case that,for instance, function is used as 'case expression', why first function couldn't be evaluated and then its result compared with the condition? Am I missing something? Thank you in advance

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