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• F# pattern matching

  - by Roger Alsing

  What would be the most effective way to express the following code? match cond.EvalBool() with | true -> match body.Eval() with | :? ControlFlowModifier as e -> match e with | Break(scope) -> e :> obj //Break is a DU element of ControlFlowModifier | _ -> next() //other members of CFM should call next() | _ -> next() | false -> null cond.EvalBool returns a boolean result where false should return null and true should either run the entire block again (its wrapped in a func called next) or if the special value of break is found, then the loop should exit and return the break value. Is there any way to compress that block of code to something smaller?

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• "Pattern matching" of algebraic type data constructors

  - by jetxee

  Let's consider a data type with many constructors: data T = Alpha Int | Beta Int | Gamma Int Int | Delta Int I want to write a function to check if two values are produced with the same constructor: sameK (Alpha _) (Alpha _) = True sameK (Beta _) (Beta _) = True sameK (Gamma _ _) (Gamma _ _) = True sameK _ _ = False Maintaining sameK is not much fun, it is potentially buggy. For example, when new constructors are added to T, it's easy to forget to update sameK. I omitted one line to give an example: -- it’s easy to forget: -- sameK (Delta _) (Delta _) = True The question is how to avoid boilerplate in sameK? Or how to make sure it checks for all T constructors? The workaround I found is to use separate data types for each of the constructors, deriving Data.Typeable, and declaring a common type class, but I don't like this solution, because it is much less readable and otherwise just a simple algebraic type works for me: {-# LANGUAGE DeriveDataTypeable #-} import Data.Typeable class Tlike t where value :: t -> t value = id data Alpha = Alpha Int deriving Typeable data Beta = Beta Int deriving Typeable data Gamma = Gamma Int Int deriving Typeable data Delta = Delta Int deriving Typeable instance Tlike Alpha instance Tlike Beta instance Tlike Gamma instance Tlike Delta sameK :: (Tlike t, Typeable t, Tlike t', Typeable t') => t -> t' -> Bool sameK a b = typeOf a == typeOf b

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• OpenCV shape matching

  - by MAckerman

  I'm new to OpenCV (am actually using Emgu CV C# wrapper) and am attempting to do some object detection. I'm attempting to determine if an object matches a predefined set of objects (that I will have to define). The background is well lit and does not move. My objects that I am starting with are bottles and cans. My current approach is: Do absDiff with a previously taken background image to separate the background. Then dilate 4x to make the lighter areas (in labels) shrink. Then I do a binary threshold to get a big blog, followed by finding contours in this image. I then take the largest contour and draw it, which becomes my shape to either save to the accepted set or compare with the accepted set. Currently I'm using cvMatchShapes, but the double return value seems to vary widely. I'm guessing it is because it doesn't take into account rotation. Is this approach a good one? It isn't working well for glass bottles since the edges are hard to find... I've read about haar classifiers, but thinking that might be overkill for my task.

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• pattern matching and returning new object based on pattern

  - by Rune FS

  Say I'v got some code like this match exp with | Addition(lhs,rhs,_) -> Addition(fix lhs,fix rhs) | Subtraction(lhs,rhs,_) -> Subtraction(fix lhs,fix rhs) is there any way that would allow me to do something like match exp with | Addition(lhs,rhs,_) | Subtraction(lhs,rhs,_) -> X(fix lhs,fix rhs) where X be based on the actual pattern being matched

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• Excel Matching problem with logic expression

  - by abelenky

  (I understand Excel is only borderline programming) I have a block of data that represents the steps in a process and the possible errors: ProcessStep Status FeesPaid OK FormRecvd OK RoleAssigned OK CheckedIn Not Checked In. ReadyToStart Not Ready for Start I want to find the first Status that is not "OK". I have attempted this: =Match("<>""OK""", StatusRange, 0) which is supposed to return the index of the first element in the range that is NOT-EQUAL (<) to "OK" But this doesn't work, instead returning #N/A. I expect it to return 4 (index #4, in a 1-based index, representing that CheckedIn is the first non-OK element) Any ideas how to do this?

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• Regex and Pattern Matching in Scala

  - by Bruce Ferguson

  I am not strong in regex, and pretty new to Scala. I would like to be able to find a match between the first letter of a word, and one of the letters in a group such as "ABC". In pseudocode, this might look something like: case Process(word) => word.firstLetter match { case([a-c][A-C]) => case _ => } } but I don't know how to grab the first letter in Scala instead of Java, how to express the regular expression properly, nor if it's possible to do this within a case class. Any suggestions? Thanks in advance. Bruce

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• Python: Elegant way to check if at least one regex in list matches a string

  - by houbysoft

  Hi. I have a list of regexes in python, and a string. Is there an elegant way to check if the at least one regex in the list matches the string? By elegant, I mean something better than simply looping through all of the regexes and checking them against the string and stopping if a match is found. Basically, I had this code: list = ['something','another','thing','hello'] string = 'hi' if string in list: pass # do something else: pass # do something else Now I would like to have some regular expressions in the list, rather than just strings, and I am wondering if there is an elegant solution to check for a match to replace if string in list:. Thanks in advance.

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• F# pattern matching when mixing DU's and other values

  - by Roger Alsing

  What would be the most effective way to express the following code? match cond.EvalBool() with | true -> match body.Eval() with | :? ControlFlowModifier as e -> match e with | Break(scope) -> e :> obj //Break is a DU element of ControlFlowModifier | _ -> next() //other members of CFM should call next() | _ -> next() //all other values should call next() | false -> null cond.EvalBool returns a boolean result where false should return null and true should either run the entire block again (its wrapped in a func called next) or if the special value of break is found, then the loop should exit and return the break value. Is there any way to compress that block of code to something smaller?

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• Replace whitespaces using PHP preg_replace function ignoring quoted strings

  - by Saiful

  Look at the following string: SELECT column1 , column2, column3 FROM table1 WHERE column1 = 'text, "FROM" \'from\\\' x' AND column2 = "sample text 'where' \"where\\\" " AND ( column3 = 5 ) I need to escape unnecessary white space characters from the string like: removing white space from beginning and ending position of , ( ) etc removing newline (\r\n) and tabs (\t) But one thing. The remove process could not remove white spaces from the quoted string like: 'text, "FROM" \'from\\' x' "sample text 'where' \"where\\" " etc. i need to use the PHP function: preg_replace($pattern, $replacement, $string); So what will be the value of $pattern and $replacement where the value of $string is the given SQL.

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• Eliminating matching values in a SQL result set

  - by Burgess Taylor

  I have a table with a list of transactions (invoices and credits) and I need to get a list of all the rows where the invoices and credits don't match up. eg user product value bill ThingA 200 jim ThingA -200 sue ThingB 100 liz ThingC 50 I only want to see the third and fourth rows, as the values of the others match off. I can do this if I select product, sum(value) ... group by product having sum(value) < 0 which works well, but I want to return the user name as well. As soon as I add the user to the select, I need to group by it as well, which messes it up as the amounts don't match up by user AND product. Any ideas ? I am using MS SQL 2000... Cheers

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• Haskell: Pattern Matching with Lists

  - by user1670032

  I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0. Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times. changeToZero [] = [] changeToZero [x] = [x] changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws changeToZero (x:xs) = x : changeToZero xs *Main changeToZero [-1,1,-2,2,-3,3] [-1,1,-2,2,-3,3] *Main changeToZero [-2,1,2,3] [-2,1,0,3] *Main changeToZero [-2,1,2,3,2] [-2,1,0,3,2] *Main changeToZero [1,-2,2,2,1] [1,-2,2,0,1]

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• Is it possible, with simple F# pattern matching transformations, to ignore unmatched values without

  - by Phobis

  So, I previously asked this question: http://stackoverflow.com/questions/2820234/can-someone-help-me-compare-using-f-over-c-in-this-specific-example-ip-address I was looking at the posted code and I was wondering if this code could be written without it producing a warning: let [|a;b;c;d|] = s.Split [|'.'|] IP(parseOrParts a, parseOrParts b, parseOrParts c, parseOrParts d) Is it possible to do something for the match _ pattern ot ignore? Without adding in something like Active Patterns? i want to keep the code as simple as possible... can I do this without drastically changing this code? NOTE: Warning is as follows Warning Incomplete pattern matches on this expression. For example, the value '[|_; _; _; _; _|]' may indicate a case not covered by the pattern(s).

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• How to implement best matching logic in TSQL (SQL Server 2000)

  - by sanjay-kumar1911

  I have two tables X and Y: Table X C1 C2 C3 1 A 13 2 B 16 3 C 8 Table Y C1 C2 C3 C4 1 A 2 N 2 A 8 N 3 A 12 N 4 A 5 N 5 B 7 N 6 B 16 N 7 B 9 N 8 B 5 N 9 C 8 N 10 C 2 N 11 C 8 N 12 C 6 N Records in Table Y can be n number CREATE TABLE X(C1 INT, C2 CHAR(1), C3 INT); CREATE TABLE Y(C1 INT, C2 CHAR(1), C3 INT, C4 CHAR(1)); with following data: INSERT INTO X VALUES (1 'A',13 ); INSERT INTO X VALUES (2 'B',16 ); INSERT INTO X VALUES (3 'C',8 ); INSERT INTO Y VALUES (1,'A', 2,'N'); INSERT INTO Y VALUES (2,'A', 8,'N'); INSERT INTO Y VALUES (3,'A', 12,'N'); INSERT INTO Y VALUES (4,'A', 5,'N'); INSERT INTO Y VALUES (5,'B', 7,'N'); INSERT INTO Y VALUES (6,'B', 16,'N'); INSERT INTO Y VALUES (7,'B', 9,'N'); INSERT INTO Y VALUES (8,'B', 5,'N'); INSERT INTO Y VALUES (9,'C', 8,'N'); INSERT INTO Y VALUES (10,'C', 2,'N'); INSERT INTO Y VALUES (11,'C', 8,'N'); INSERT INTO Y VALUES (12,'C', 6,'N'); EXPECTED RESULT Table Y C1 C2 C3 C4 1 A 2 N 2 A 8 Y 3 A 12 N 4 A 5 Y 5 B 7 N 6 B 16 Y 7 B 9 N 8 B 5 N 9 C 8 Y 10 C 2 N 11 C 8 N 12 C 6 N How do I compare value of column C3 in Table X with all possible matches of column C3 of Table Y and to mark records as matched and unmatched in column C4 of Table Y? Possible matches for A (i.e. value of column C2 in Table X) would be (where R is row number i.e. value of column C1 in Table Y): R1, R2, R3, R4, R1+R2, R1+R3, R1+R4, R2+R3, R2+R4, R3+R4, R4+R5, R1+R2+R3, R1+R2+R4, R2+R3+R4, R1+R2+R3+R4

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• Matching a rotated bitmap to a collage image

  - by Dmi

  Hi, My problem is that I have an image of a detailed street map. On this map, there can be a certain small image of a sign (such as a traffic light icon) rotated at any angle, maybe resized. I have this small image in a bitmap. Is there any algorithm or technique by which I can locate this bitmap if a copy of it exists, rotated and maybe resized, in the large collage image? This is similar to the problem with Augmented Reality and locating the marker image, but mine is only 2D with no perspective distortion.

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• Regular expression match, extracting only wanted segments of string

  - by Ben Carey

  I am trying to extract three segments from a string. As I am not particularly good with regular expressions, I think what I have done could probably be done better... I would like to extract the bold parts of the following string: SOMETEXT: ANYTHING_HERE (Old=ANYTHING_HERE, New=ANYTHING_HERE) Some examples could be: ABC: Some_Field (Old=,New=123) ABC: Some_Field (Old=ABCde,New=1234) ABC: Some_Field (Old=Hello World,New=Bye Bye World) So the above would return the following matches: $matches[0] = 'Some_Field'; $matches[1] = ''; $matches[2] = '123'; So far I have the following code: preg_match_all('/^([a-z]*\:(\s?)+)(.+)(\s?)+\(old=(.+)\,(\s?)+new=(.+)\)/i',$string,$matches); The issue with the above is that it returns a match for each separate segment of the string. I do not know how to ensure the string is the correct format using a regular expression without catching and storing the match if that makes sense? So, my question, if not already clear, how I can retrieve just the segments that I want from the above string?

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• Strange pattern matching with functions instancing Show

  - by Sean D

  So I'm writing a program which returns a procedure for some given arithmetic problem, so I wanted to instance a couple of functions to Show so that I can print the same expression I evaluate when I test. The trouble is that the given code matches (-) to the first line when it should fall to the second. {-# OPTIONS_GHC -XFlexibleInstances #-} instance Show (t -> t-> t) where show (+) = "plus" show (-) = "minus" main = print [(+),(-)] returns [plus,plus] Am I just committing a motal sin printing functions in the first place or is there some way I can get it to match properly? edit:I realise I am getting the following warning: Warning: Pattern match(es) are overlapped In the definition of `show': show - = ... I still don't know why it overlaps, or how to stop it.

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• Implementing class for pattern matching

  - by Jeriho

  For example, val list = List(1,2,3) list match{ case a:::b => case _ => } you can match head and tail of a List using :::' or tokens of ParseResult using~'. What should I do to create class that can be matched like preceding classes?

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• How to start matching and saving matched from exact point in a text

  - by yuliya

  I have a text and I write a parser for it using regular expressions and perl. I can match what I need with two empty lines (I use regexp), because there is a pattern that allows recognize blocks of text after two empty lines. But the problem is that the whole text has Introduction part and some text in the end I do not need. Here is a code which matches text when it finds two empty lines #!/usr/bin/perl use strict; use warnings; my $file = 'first'; open(my $fh, '<', $file); my $empty = 0; my $block_num = 1; open(OUT, '>', $block_num . '.txt'); while (my $line = <$fh>) { chomp ($line); if ($line =~ /^\s*$/) { $empty++; } elsif ($empty == 2) { close(OUT); open(OUT, '>', ++$block_num . '.txt'); $empty = 0; } else { $empty = 0;} print OUT "$line\n"; } close(OUT); This is example of the text I need (it's really small :)) this is file example I think that I need to iterate over the text till the moment it will find the word LOREM IPSUM with regexps this kind "/^LOREM IPSUM/", because it is the point from which needed text starts(and save the text in one file when i reach the word). And I need to finish iterating over the text when INDEX word is fount or save the text in separate file. How could I implement it. Should I use next function to proceed with lines or what? BR, Yuliya

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• Pattern Matching of Units of Measure in F#

  - by Oldrich Svec

  This function: let convert (v: float<_>) = match v with | :? float<m> -> v / 0.1<m> | :? float<m/s> -> v / 0.2<m/s> | _ -> failwith "unknown" produces an error The type 'float<'u>' does not have any proper subtypes and cannot be used as the source of a type test or runtime coercion. Is there any way how to pattern match units of measure?

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• Fast string suffix checking in C# (.NET 4.0)?

  - by ilitirit

  What is the fastest method of checking string suffixes in C#? I need to check each string in a large list (anywhere from 5000 to 100000 items) for a particular term. The term is guaranteed never to be embedded within the string. In other words, if the string contains the term, it will be at the end of the string. The string is also guaranteed to be longer than the suffix. Cultural information is not important. These are how different methods performed against 100000 strings (half of them have the suffix): 1. Substring Comparison - 13.60ms 2. String.Contains - 22.33ms 3. CompareInfo.IsSuffix - 24.60ms 4. String.EndsWith - 29.08ms 5. String.LastIndexOf - 30.68ms These are average times. [Edit] Forgot to mention that the strings also get put into separate lists, but this is not important. It does add to the running time though. On my system substring comparison (extracting the end of the string using the String.Substring method and comparing it to the suffix term) is consistently the fastest when tested against 100000 strings. The problem with using substring comparison though is that Garbage Collection can slow it down considerably (more than the other methods) because String.Substring creates new strings. The effect is not as bad in .NET 4.0 as it was in 3.5 and below, but it is still noticeable. In my tests, String.Substring performed consistently slower on sets of 12000-13000 strings. This will obviously differ between systems and implementations. [EDIT] Benchmark code: http://pastebin.com/smEtYNYN

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• Advice on String Similarity Metrics (Java). Distance, sounds like or combo?

  - by andreas

  Hello, A part of a process requires to apply String Similarity Algorithms. The results of this process will be stored and produce lets say SS_Dataset. Based on this Dataset, further decisions will have to be made. My questions are: Should i apply one or more string similarity algorithms to produce SS_Dataset ? Any comparisons between algorithms that calculate the 'distance' and the 'Sounds Like' similarity ? Does one family of algorithms produces more accurate results over the other? Does a combination give more accurate results on similarity? Can you recommend implementations that you have worked with? My implementation will include packages from the following libraries http://www.dcs.shef.ac.uk/~sam/simmetrics.html http://jtmt.sourceforge.net/ Regards,

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• Delphi Unicode String Type Stored Directly at its Address

  - by Andreas Rejbrand

  I want a string type that is Unicode and that stores the string directly at the adress of the variable, as is the case of the (Ansi-only) ShortString type. I mean, if I declare a S: ShortString and let S := 'My String', then, at @S, I will find the length of the string (as one byte, so the string cannot contain more than 255 characters) followed by the ANSI-encoded string itself. What I would like is a Unicode variant of this. That is, I want a string type such that, at @S, I will find a unsigned 32-bit integer containing the length of the string in bytes (or in characters, which is half the number of bytes) followed by the Unicode representation of the string. I have tried WideString, UnicodeString, and RawByteString, but they all appear only to store an adress at @S, and the actual string somewhere else (I guess this has do do with reference counting and such). I suspect that there is no built-in type to use, and that I have to come up with my own way of storing text the way I want (which actually is fun). Am I right?

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• Insert string between two markers

  - by user275074

  I have a requirement to insert a string between two markers. Initially I get a sting (from a file stored on the server) between #DATA# and #END# using: function getStringBetweenStrings($string,$start,$end){ $startsAt=strpos($string,$start)+strlen($start); $endsAt=strpos($string,$end, $startsAt); return substr($string,$startsAt,$endsAt-$startsAt); } I do some processing and based on the details of the string, query for some records. If there are records I need to be able to append them at the end of the string and then re-insert the string between #DATA# and #END# within the file on the server. How can I best achieve this? Is it possible to insert a record at a time in the file before #END# or is it best to manipulate the string on the server and just re-insert over the existing string in the file on the server?

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• how to retrieve part of a string in java?

  - by mithun1538

  Hello everyone, I am designing a chat applet. In this, a user will append his name to the beginning of the message that he sends to the other user. In the window of other user, I want to retrieve the appended user name from that string. How do I do that? The message sent by the user is as follows : final_msg = user_name + ": " + user_message Hence I want to know how to retrieve the user_name string only. Is there a function that can retrieve a substring upto the first ":"? I dont want to use final_msg.split(":"), because there is a possiblity that the user_message contains ":", which will then give me an array of strings.

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• How to do this Python / MySQL manipulation (match) more efficiently?

  - by NJTechie

  Following is my data : Company Table : ID Company Address City State Zip Phone 1 ABC 123 Oak St Philly PA 17542 7329878901 2 CDE 111 Joe St Newark NJ 08654 3 GHI 211 Foe St Brick NJ 07740 7321178901 4 JAK 777 Wall Ocean NJ 07764 7322278901 5 KLE 87 Ilk St Plains NY 07654 7376578901 6 AB 1 W.House SField PA 87656 7329878901 Branch Office Table : ID Address City State Zip Phone 1 323 Alk St Philly PA 17542 7329832221 1 171 Joe St Newark NJ 08654 3 287 Foe St Brick NJ 07740 7321178901 3 700 Wall Ocean NJ 07764 7322278901 1 89 Blk St Surrey NY 07154 7376222901 File to be Matched (In MySQL): ID Company Address City State Zip Phone 1 ABC 123 Oak St Philly PA 17542 7329878901 2 AB 171 Joe St Newark NJ 08654 3 GHI 211 Foe St Brick NJ 07740 7321178901 4 JAK 777 Wall Ocean NJ 07764 7322278901 5 K 87 Ilk St Plains NY 07654 7376578901 Resulting File : ID Company Address City State Zip Phone appendedID 1 ABC 123 Oak St Philly PA 17542 7329878901 [Original record, field always empty] 1 ABC 171 Joe St Newark NJ 08654 1 [Company Table] 1 ABC 323 Alk St Philly PA 17542 7329832221 1 [Branch Office Table] 1 AB 1 W.House SField PA 87656 7329878901 6 [Partial firm and State, Zip match] 2 CDE 111 Joe St Newark NJ 08654 3 GHI 211 Foe St Brick NJ 07740 7321178901 3 GHI 700 Wall Ocean NJ 07764 7322278901 3 3 GHI 287 Foe St Brick NJ 07740 7321178901 3 4 JAK 777 Wall Ocean NJ 07764 7322278901 5 KLE 87 Ilk St Surrey NY 07654 7376578901 5 KLE 89 Blk St Surrey NY 07154 7376222901 5 Requirement : 1) I have to match each firm on the 'File to be Matched' to that of Company and Branch Office tables (MySQL). 2) If there are multiple exact/partial matches, then the ID from Company, Branch Office table is inserted as a new row in the resulting file. 3) Not all the firms will be matched perfectly, in that case I have to match on partial Company names (like 5/8th of the company name) and any of the address fields and insert them in the resulting file. Please help me out in the most efficient solution for this problem.

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