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• Javscript filter vs map problem

  - by graham.reeds

  As a continuation of my min/max across an array of objects I was wondering about the performance comparisons of filter vs map. So I put together a test on the values in my code as was going to look at the results in FireBug. This is the code: var _vec = this.vec; min_x = Math.min.apply(Math, _vec.filter(function(el){ return el["x"]; })); min_y = Math.min.apply(Math, _vec.map(function(el){ return el["x"]; })); The mapped version returns the correct result. However the filtered version returns NaN. Breaking it out, stepping through and finally inspecting the results, it would appear that the inner function returns the x property of _vec but the actual array returned from filter is the unfiltered _vec. I believe my usage of filter is correct - can anyone else see my problem?

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• Comparing numeric strings

  - by Kiren Siva

  From the question PHP Type-Juggling and (strict) Greater/Lesser Than Comparisons I know PHP interpret strings as numbers whenever it can. "10" < "1a" => 10 less than 1 expecting false "1a" < "2" => 1 less than 2 expecting true "10" > "2" => 10 greater than 2 expecting true But in the case of "10" < "1a" php returns true. I am not understanding the concept please help me to clarify it. Edit: But when I add "10" + "1a" it returns 11 that means php interprets "10" as 10 and "1a" as 1. Is that correct?

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• Write a function in c that includes the following sequence of statements [Wont Compile]

  - by Cody

  There is a question in my programming languages textbook that is as follows: Write a C function that includes the following sequence of statements: x = 21; int x; x = 42; Run the program and explain the results. Rewrite the same code in C++ and Java and compare the results. I have written code, and played with it in all three languages but I can not even get it to compile. This includes declaring x above the three lines as well as in the calling function (as this question is obviously attempting to illustrate scoping issues) I'd like to explain the results and do the comparisons on my own, as it is an assignment question but I was wondering if anyone had any insight as to how to get this code to compile? Thanks

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• In C, would !~b ever be faster than b == 0xff ?

  - by James Morris

  From a long time ago I have a memory which has stuck with me that says comparisons against zero are faster than any other value (ahem Z80). In some C code I'm writing I want to skip values which have all their bits set. Currently the type of these values is char but may change. I have two different alternatives to perform the test: if (!~b) /* skip */ and if (b == 0xff) /* skip */ Apart from the latter making the assumption that b is an 8bit char whereas the former does not, would the former ever be faster due to the old compare to zero optimization trick, or are the CPUs of today way beyond this kind of thing?

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• Boolean Not operator in VBScript

  - by Lumi

  Consider the following two conditionals (involving bitwise comparisons) in VBScript: If 1 And 3 Then WScript.Echo "yes" Else WScript.Echo "no" If Not(1 And 3) Then WScript.Echo "yes" Else WScript.Echo "no" Prints first yes, then no, right? cscript not.vbs Wrong! It prints yes twice! Wait a second, the Not operator is supposed to perform logical negation on an expression. The logical negation of true is false, as far as I know. Must I conclude that it doesn't live up to that promise? How and why and what is going on here? What is the rationale, if any?

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• Method return values and exceptions

  - by dnagirl

  I have an interface called iIncident which defines a single method when(). when() should return a DateTime object. I'm trying to decide what to do if $object->when() has no DateTime to return as might be the case just after an object is instantiated and before all its properties are set. My choices are: return false throw some kind of Exception return some default DateTime like '9999-01-01' My inclination is to go with an Exception since $object really can't act as an incident until it knows when it occurred. I don't want to return a default DateTime because it complicates comparisons and it's not true. And I don't really want to return false because then I have to check for it every time I call the method- but if that is the preferred method, I guess I will. Is throwing an exception the best way? And is there a predefined exception type I should use (none of the SPL ones struck me as particularly appropriate- but that might just indicate my lack of experience)?

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• direct access to vector elements similar to arrays

  - by mixm

  hi. im currently creating a tile based game, where elements of the games are placed in four different vectors (since there are multiple game objects with different properties, hence stored in different vectors). these game elements themselves contain x and y coordinates similar to how they are stored in a two dimensional array. i was wondering if there was a way to access these vector elements similar to two dimensional array access (currently i am implementing an for loop to cycle the elements while comparing its coordinates). this kinda sucks when i need to refresh my display at every game cycle (since the large number of comparisons and loops). im implementing this in java btw.

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• Determining whether a file is a duplicate

  - by Todd R

  Is there a reliable way to determine whether or not two files are the same? For example, two files with the same size and type may or may not be the same binarilly (yeah, I know it's not really a word). I assume that comparing one or two checksums of the files will help, but I wonder: How reliable are checksums at determining whether two files are different; what are the chances of two different files having the same checksum? Would reliability increase by applying additional checksum comparisons? Which checksum algorithm(s) would be the most efficient and/or reliable? Any ideas, suggestions or thoughts are appreciated! P.S. The code for this is being written in Java running on a nix system, but generic or platform agnostic input is most helpful.

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• Create function in python to find the highest of all function arguments, and return the "tag" of the value.

  - by gatechgrad

  Consider the following: p1=1; p2=5; p3=7; highest=max(p1,p2,p3). The max function would return 7. I am looking to create a similar function, which would return "p3". I have created a small function (by simple comparisons) for the above example, shown below. however I am having trouble when the number of arguments go up. def highest(p1,p2,p3) if (p1p2) and (p1p3): return "p1" if (p2p1) and (p2p3): return "p2" if (p3p1) and (p3p1): return "p3". Is there a simpler way to do this

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• Optimize Binary Search Algorithm

  - by Ganesh M

  In a binary search, we have two comparisons one for greater than and other for less than, otherwise its the mid value. How would you optimize so that we need to check only once? bool binSearch(int array[], int key, int left, int right) { mid = left + (right-left)/2; if (key < array[mid]) return binSearch(array, key, left, mid-1); else if (key > array[mid]) return binSearch(array, key, mid+1, right); else if (key == array[mid]) return TRUE; // Found return FALSE; // Not Found }

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• Generate a collection of changed lines between two revisions of a file using Java

  - by mchr

  I am writing an eclipse plugin which needs to be able to determine which lines of a file have changed compared to a different version of the same file. Is there an existing class or library which I can use for this task? The closest I have found is org.eclipse.compare.internal.merge.DocumentMerger. This can be used to find the information I need but is in an internal package so is not suitable for me to use. I could copy/paste the source of this class and adapt it to my requirements. However, I am hoping there is an existing library to handle textual comparisons.

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• Masking a bit in C returning unexpected result

  - by Eamorr

  0x7F000000 is 0111 1111 0000 0000 0000 0000 0000 0000 in 32 bit binary. 0x01000058 is 0000 0001 0000 0000 0000 0000 0101 1000. When I AND the two numbers together I expect 0000 0001 0000 0000 0000 0000 0000 0000, but for some reason I get 0. Here is my code: #define MASK_binop 0x80000000 #define MASK_operation 0x7F000000 int instruction=atoi(line); if((MASK_binop & instruction)>0) printf("binop\n"); else if((MASK_operation & instruction)>0) printf("operation\n"); Each of the above comparisons keeps returning zero. Is it something to do with 32/64 bits? I'm using 64-bit compiler.

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• How can I compute the average cost for this solution of the element uniqueness problem?

  - by Alceu Costa

  In the book Introduction to the Design & Analysis of Algorithms, the following solution is proposed to the element uniqueness problem: ALGORITHM UniqueElements(A[0 .. n-1]) // Determines whether all the elements in a given array are distinct // Input: An array A[0 .. n-1] // Output: Returns "true" if all the elements in A are distinct // and false otherwise. for i := 0 to n - 2 do for j := i + 1 to n - 1 do if A[i] = A[j] return false return true How can I compute the average cost (i.e. number of comparisons for a given n) for this algorithm? What is a reasonable assumption about the input?

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• Comparison question string vs int

  - by Mike

  Can someone explain to me why these comparisons work they way the do. I had a bug in one of my scripts that took me a little bit to work through. I was using read-host and typing a number. It was storing it as a string. Write-Host "(`'2`' -gt 9 ) = " ('2' -gt 9 ) Write-Host "(2 -gt 9 ) = " (2 -gt 9 ) Write-Host "(`'2`' -gt 10 ) = " ('2' -gt 10 ) If you are comparing a string to an Int does it use the Ascii value? If so why does the first one show $false, it should be $true. Then how is it when you chage it to an int of 10 it because $true.

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• find all occurrences of comparison with == in visual studio

  - by Emiswelt

  Hi there I made the mistake of using == for comparing IP addresses instead of using the equals() method of the IPAddress class in C#, which will result in the comparison of references instead of values. Since the solution I am currently working on is very large for a one-man project ( 100.000 lines of source code), I am very sure that I still have some of these wrong statements in my code. Is there any possibility to tell Visual Studio to find all occurrences of == operations on a specific class for me, so that I can find and clean up the bugged comparisons? with best regards, emi

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• Best way to search a point across several polygons

  - by user1474341

  I have a requirement whereby I need to match a given point (lat,lon) against several polygons to decide if there is a match. The easiest way would be to iterative over each polygon and apply the point-in-polygon check algorithm, but that is prohibitively expensive. The next optimization that I did was to define a bounding rectangle for each polygon (upper bound, lower bound) and iteratively check the point against the bounding box (fewer comparisons as against checking all the points in the polygon). Is there any other optimization possible? Would a spatial index on the bound rectangle points or a geohash help ? Any guidance would be greatly appreciated. Thanks!

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• Knowledge mining using Hadoop.

  - by Anurag

  Hello there, I want to do a project Hadoop and map reduce and present it as my graduation project. To this, I've given some thought,searched over the internet and came up with the idea of implementing some basic knowledge mining algorithms say on a social websites like Facebook or may stckoverflow, Quora etc and draw some statistical graphs, comparisons frequency distributions and other sort of important values.For searching purpose would it be wise to use Apache Solr ? I want know If such thing is feasible using the above mentioned tools, if so how should I build up on this little idea? Where can I learn about knowledge mining algorithms which are easy to implement using java and map reduce techniques? In case this is a wrong idea please suggest what else can otherwise be done on using Hadoop and other related sub-projects? Thank you

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• Birthday effect - clarification needed plz.

  - by Mark

  Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: 1) Pick any message m and compute h(m). 2) Update list L. Check if h(m) is in the list L. 3) if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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• client-side vs server-side

  - by amalafrida

  In general, should one design in order to place processing load on client-side? More specifically, a search engine to locate subscriber information requires a fair amount of parsing (multiple phone numbers to sort and format, hour of day, timezone, comparisons for possible substitutions of user information, etc.). Again, in general, is it preferred that one have client-side do the work? It seems to me 'yes' in a situation in which one will have many thousands of hits per minute. Use php for quick database queries ... process retrieved data client-side. yes ... no?

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• Django Project Done and Working. Now What?

  - by Rodrogo

  Hi, I just finished what I would call a small django project and pretty soon it's going live. It's only 6 models but a fairly complex view layer and a lot of records saving and retrieving. Of course, forgetting the obvious huge amount of bugs that will, probably, fill my inbox to the top, what would it be the next step towards a website with best performance. What could be tweaked? I'm using jmeter a lot recently and feel confident that I have a good baseline for future performance comparisons, but the thing is: I'm not sure what is the best start, since I'm a greedy bastard that wants to work the least possible and gather the best results. For instance, should I try an approach towards infrastructure, like a distributed database, or should I go with the code itself and in that case, is there something that specifically results in better performance? In your experience, whats pays off more? Personal anecdotes are welcome, but some fact based opinions are even more. :) Thanks very much.

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• Can someone please clarify the Birthday Effect for me?

  - by Mark

  Please help interpret the Birthday effect as described in Wikipedia: A birthday attack works as follows: Pick any message m and compute h(m). Update list L. Check if h(m) is in the list L. if (h(m),m) is already in L, a colliding message pair has been found. else save the pair (h(m),m) in the list L and go back to step 1. From the birthday paradox we know that we can expect to find a matching entry, after performing about 2^(n/2) hash evaluations. Does the above mean 2^(n/2) iterations through the above entire loop (i.e. 2^(n/2) returns to step 1), OR does it mean 2^(n/2) comparisons to individual items already in L.

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• compare two characters based on subset

  - by schultem

  I have a simple dataframe with two columns: df <- data.frame(x = c(1,1,2,2,3), y = c(rep(1:2,2),1), target = c('a','a','a','b','a')) I would like to compare the strings in the target column (find out whether they are equal or not, i.e., TRUE or FALSE) within every level of x (same number for x). First I would like to compare lines 1 and 2, then 3 and 4 ... My problem is that I am missing some comparisons, for example, line 5 has only one case instead of two - so it should turn out to be FALSE. Variable y indicates the first and second case within x. I played around with ddply doing something like: ddply(df, .(x), summarise, ifelse(as.character(df[df$y == '1',]$target), as.character(df[df$y == '2',]$target),0,1)) which is ugly ... and does not work ... Any insights how I could achieve this comparison? Thanks

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• Why does SQL Server consider N'????' and N'???' to be equal?

  - by Aidan Ryan

  We are testing our application for Unicode compatibility and have been selecting random characters outside the Latin character set for testing. On both Latin and Japanese-collated systems the following equality is true (U+3422): N'????' = N'???' but the following is not (U+30C1): N'????' = N'???' This was discovered when a test case using the first example (using U+3422) violated a unique index. Do we need to be more selective about the characters we use for testing? Obviously we don't know the semantic meaning of the above comparisons. Would this behavior be obvious to a native speaker?

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• Programmable Home Security Alarm [closed]

  - by stej

  I don't ask for recommendation! (just wanted to say that; anyway it doesn't matter now as the question is closed) I've seen some advertisements about home alarms that notifies me that something is happening in my house. None of them mentioned programmability (with real programming language like e.g C, assembler, whatever). As a programmer I'd like to have a possibility to add some behaviour, that is not part of the alarm itself. This might be: take snapshots of all cameras in a house and send it to some email send email, twitter message, skype message to some predefined account send email to a police (silly, I know) start turning the lights on and off (scary, right?) etc. (would be veeery challenging with assembler, I know; but lets suppose I can use some more high level language) I don't expect that there is a alarm system capable of this stuff, that's why I'm looking for a programmable module. Question: Is it even possible? Is it good idea (my program could crash and cause instability of the system).

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• How do Opera's keyboard shortcut settings work?

  - by zem

  Firefox 4 beta is starting to freeze up the way Firefox 3 used to on my machine, and I want a browser that'll play gifs at full speed, so on a Mac my only other choice seems to be Opera. There are just two issues I have with it right now: one, the scrolling is weird compared to every other Mac application, but I can get used to that if there's no way to fix it. Two, cmd-1 through cmd-9 activate the "speed dial" bookmarks instead of selecting tabs 1-9, like in Firefox and Chrome. I can disable those shortcuts easily enough, so I don't keep accidentally loading a different page when I instinctively try to do that, but in an ideal world I could remap those commands to do what I want. The keyboard shortcut editor is weird: There seems to be a scrappy little language for associating actions with commands. It has some limited autocompletion when you type stuff in, and I couldn't find a "select specific tab" action, but some of the existing commands are complicated enough that I'd be surprised if there's not a way to do it. Is there documentation for this language anywhere? Clicking "help" just brings me to this page, which is not very helpful.

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