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• Is there a Boost (or other common lib) type for matrices with string keys?

  - by mohawkjohn

  I have a dense matrix where the indices correspond to genes. While gene identifiers are often integers, they are not contiguous integers. They could be strings instead, too. I suppose I could use a boost sparse matrix of some sort with integer keys, and it wouldn't matter if they're contiguous. Or would this still occupy a great deal of space, particularly if some genes have identifiers that are nine digits? Further, I am concerned that sparse storage is not appropriate, since this is an all-by-all matrix (there will be a distance in each and every cell, provided the gene exists). I'm unlikely to need to perform any matrix operations (e.g., matrix multiplication). I will need to pull vectors out of the matrix (slices). It seems like the best type of matrix would be keyed by a Boost unordered_map (a hash map), or perhaps even simply an STL map. Am I looking at this the wrong way? Do I really need to roll my own? I thought I saw such a class somewhere before. Thanks!

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• C# wrapper for array of three pointers

  - by fergs

  I'm currently working on a C# wrapper to work with Dallmeier Common API light. See previous posting: http://stackoverflow.com/questions/2430089/c-wrapper-and-callbacks I've got pretty much everything 'wrapped' but I'm stuck on wrapping a callback which contains an array of three pointers & an array integers: dlm_setYUVDataCllback int(int SessionHandle, void (*callback) (long IPlayerID, unsigned char** yuvData, int* pitch, int width, int height, int64_t ts, char* extData)) Function Set callback, to receive current YUV image. Arguments SessionHandle: handle to current session. Return PlayerID (see callback). Callback - IPlayerId: id to the Player object - yuvData: array of three pointers to Y, U and V part of image The YUV format used is YUV420 planar (not packed). char *y = yuvData[0]; char *u = yuvData[1]; char *v = yuvData[2]; - pitch: array of integers for pitches for Y, U and V part of image - width: intrinsic width of image. - height - ts : timestamp of current frame - extData: additional data to frame How do I go about wrapping this in c#? Any help is much appreciated.

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• SQL using sum to count results of multiple subqueries

  - by asdas

  I have a table with 2 columns: integer and var char. I am given only the integer values but need to do work on the var char (string) values. Given an integer, and a list of other integers (no overlap), I want to find the string for that single integer. Then I want to take that string and do the INSTR command with that string, and all the other strings for all the other integers. Then I want the sum of all the INSTR so the result is one number. So lets say I have int x, and list y=[y0, y1, y2]. I want to do 3 INSTR commands like SUM(INSTR(string for x, string for y0), INSTR(string for x, string for y1), INSTR(string for x, string for y2)) I think im going in the wrong direction, this is what I have. Im not good with sub queries. SELECT SUM ( SELECT INSTR ( SELECT string FROM pages WHERE int=? LIMIT 1, ( SELECT string FROM pages WHERE id=? OR id=? OR id=? LIMIT 3 ) ) )

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• Getting zeros between data while reading a binary file in C

  - by indiajoe

  I have a binary data which I am reading into an array of long integers using a C programme. hexdump of the binary data shows, that after first few data points , it starts again at a location 20000 hexa adresses away. hexdump output is as shown below. 0000000 0000 0000 0000 0000 0000 0000 0000 0000 * 0020000 0000 0000 0053 0000 0064 0000 006b 0000 0020010 0066 0000 0068 0000 0066 0000 005d 0000 0020020 0087 0000 0059 0000 0062 0000 0066 0000 ........ and so on... But when I read it into an array 'data' of long integers. by the typical fread command fread(data,sizeof(*data),filelength/sizeof(*data),fd); It is filling up with all zeros in my data array till it reaches the 20000 location. After that it reads in data correctly. Why is it reading regions where my file is not there? Or how will I make it read only my file, not anything inbetween which are not in file? I know it looks like a trivial problem, but I cannot figure it out even after googling one night.. Can anyone suggest me where I am doing it wrong? Other Info : I am working on a gnu/linux machine. (slax-atma distro to be specific) My C compiler is gcc.

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• How can you transform a set of numbers into mostly whole ones?

  - by Alice

  Small amount of background: I am working on a converter that bridges between a map maker (Tiled) that outputs in XML, and an engine (Angel2D) that inputs lua tables. Most of this is straight forward However, Tiled outputs in pixel offsets (integers of absolute values), while Angel2D inputs OpenGL units (floats of relative values); a conversion factor between these two is needed (for example, 32px = 1gu). Since OpenGL units are abstract, and the camera can zoom in or out if the objects are too small or big, the actual conversion factor isn't important; I could use a random number, and the user would merely have to zoom in or out. But it would be best if the conversion factor was selected such that most numbers outputted were small and whole (or fractions of small whole numbers), because that makes it easier to work with (and the whole point of the OpenGL units is that they are easy to work with). How would I find such a conversion factor reliably? My first attempt was to use the smallest number given; this resulted in no fractions below 1, but often lead to lots of decimal places where the factors didn't line up. Then I tried the mode of the sequence, which lead to the largest number of 1's possible, but often lead to very long floats for background images. My current approach gets the GCD of the whole sequence, which, when it works, works great, but can easily be thrown off course by a single bad apple. Note that while I could easily just pass the numbers I am given along, or pick some fixed factor, or use one of the conversions I specified above, I am looking for a method to reliably scale this list of integers to small, whole numbers or simple fractions, because this would most likely be unsurprising to the end user; this is not a one off conversion. The end users tend to use 1.0 as their "base" for manipulations (because it's simple and obvious), so it would make more sense for the sizes of entities to cluster around this.

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• Recursion in assembly?

  - by Davis

  I'm trying to get a better grasp of assembly, and I am a little confused about how to recursively call functions when I have to deal with registers, popping/pushing, etc. I am embedding x86 assembly in C++. Here I am trying to make a method which given an array of integers will build a linked list containing these integers in the order they appear in the array. I am doing this by calling a recursive function: insertElem (struct elem *head, struct elem *newElem, int data) -head: head of the list -data: the number that will be inserted at the end of a list -newElem: points to the location in memory where I will store the new element (data field) My problem is that I keep overwriting the registers instead of a typical linked list. For example, if I give it an array {2,3,1,8,3,9} my linked-list will return the first element (head) and only the last element, because the elements keep overwriting each other after head is no longer null. So here my linked list looks something like: 2--9 instead of 2--3--1--8--3--9 I feel like I don't have a grasp on how to organize and handle the registers. newElem is in EBX and just keeps getting rewritten. Thanks in advance!

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• [C++][OpenMP] Proper use of "atomic directive" to lock STL container

  - by conradlee

  I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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• Refactoring code/consolidating functions (e.g. nested for-loop order)

  - by bmay2

  Just a little background: I'm making a program where a user inputs a skeleton text, two numbers (lower and upper limit), and a list of words. The outputs are a series of modifications on the skeleton text. Sample inputs: text = "Player # likes @." (replace # with inputted integers and @ with words in list) lower = 1 upper = 3 list = "apples, bananas, oranges" The user can choose to iterate over numbers first: Player 1 likes apples. Player 2 likes apples. Player 3 likes apples. Or words first: Player 1 likes apples. Player 1 likes bananas. Player 1 likes oranges. I chose to split these two methods of outputs by creating a different type of dictionary based on either number keys (integers inputted by the user) or word keys (from words in the inputted list) and then later iterating over the values in the dictionary. Here are the two types of dictionary creation: def numkey(dict): # {1: ['Player 1 likes apples', 'Player 1 likes...' ] } text, lower, upper, list = input_sort(dict) d = {} for num in range(lower,upper+1): l = [] for i in list: l.append(text.replace('#', str(num)).replace('@', i)) d[num] = l return d def wordkey(dict): # {'apples': ['Player 1 likes apples', 'Player 2 likes apples'..] } text, lower, upper, list = input_sort(dict) d = {} for i in list: l = [] for num in range(lower,upper+1): l.append(text.replace('#', str(num)).replace('@', i)) d[i] = l return d It's fine that I have two separate functions for creating different types of dictionaries but I see a lot of repetition between the two. Is there any way I could make one dictionary function and pass in different values to it that would change the order of the nested for loops to create the specific {key : value} pairs I'm looking for? I'm not sure how this would be done. Is there anything related to functional programming or other paradigms that might help with this? The question is a little abstract and more stylistic/design-oriented than anything.

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• Randomly sorting an array

  - by Cam

  Does there exist an algorithm which, given an ordered list of symbols {a1, a2, a3, ..., ak}, produces in O(n) time a new list of the same symbols in a random order without bias? "Without bias" means the probability that any symbol s will end up in some position p in the list is 1/k. Assume it is possible to generate a non-biased integer from 1-k inclusive in O(1) time. Also assume that O(1) element access/mutation is possible, and that it is possible to create a new list of size k in O(k) time. In particular, I would be interested in a 'generative' algorithm. That is, I would be interested in an algorithm that has O(1) initial overhead, and then produces a new element for each slot in the list, taking O(1) time per slot. If no solution exists to the problem as described, I would still like to know about solutions that do not meet my constraints in one or more of the following ways (and/or in other ways if necessary): the time complexity is worse than O(n). the algorithm is biased with regards to the final positions of the symbols. the algorithm is not generative. I should add that this problem appears to be the same as the problem of randomly sorting the integers from 1-k, since we can sort the list of integers from 1-k and then for each integer i in the new list, we can produce the symbol ai.

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• Looking for Go equivalent of scanf.

  - by Stephen Hsu

  I'm looking for the Go equivalent of scanf(). I tried with following code: 1 package main 2 3 import ( 4 "scanner" 5 "os" 6 "fmt" 7 ) 8 9 func main() { 10 var s scanner.Scanner 11 s.Init(os.Stdin) 12 s.Mode = scanner.ScanInts 13 tok := s.Scan() 14 for tok != scanner.EOF { 15 fmt.Printf("%d ", tok) 16 tok = s.Scan() 17 } 18 fmt.Println() 19 } I run it with input from a text with a line of integers. But it always output -3 -3 ... And how to scan a line composed of a string and some integers? Changing the mode whenever encounter a new data type? The Package documentation: Package scanner A general-purpose scanner for UTF-8 encoded text. But it seems that the scanner is not for general use. Updated code: func main() { n := scanf() fmt.Println(n) fmt.Println(len(n)) } func scanf() []int { nums := new(vector.IntVector) reader := bufio.NewReader(os.Stdin) str, err := reader.ReadString('\n') for err != os.EOF { fields := strings.Fields(str) for _, f := range fields { i, _ := strconv.Atoi(f) nums.Push(i) } str, err = reader.ReadString('\n') } r := make([]int, nums.Len()) for i := 0; i < nums.Len(); i++ { r[i] = nums.At(i) } return r }

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• Database locking: ActiveRecord + Heroku

  - by JP

  I'm building a Sinatra based app for deployment on Heroku. You can imagine it like a standard URL shortener but where old shortcodes expire and become available for new URLs (I realise this is a silly concept but its easier to explain this way). I'm representing the shortcode in my database as an integer and redefining its reader to give a nice short and unique string from the integer. As some rows will be deleted, I've written code that goes thru all the shortcode integers and picks the first free one to use just before_save. Unfortunately I can make my code create two rows with identical shortcode integers if I run two instances very quickly one after another, which is obviously no good! How should I implement a locking system so that I can quickly save my record with a unique shortcode integer? Here's what I have so far: Chars = ('a'..'z').to_a + ('A'..'Z').to_a + ('0'..'9').to_a CharLength = Chars.length class Shorts < ActiveRecord::Base before_save :gen_shortcode after_save :done_shortcode def shortcode i = read_attribute(:shortcode).to_i return '0' if i == 0 s = '' while i > 0 s << Chars[i.modulo(CharLength)] i /= 62 end s end private def gen_shortcode shortcode = 0 self.class.find(:all,:order=>"shortcode ASC").each do |s| if s.read_attribute(:shortcode).to_i != shortcode # Begin locking? break end shortcode += 1 end write_attribute(:shortcode,shortcode) end def done_shortcode # End Locking? end end

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• Tips for submitting a library to Boost?

  - by AraK

  Hi everyone, Summer is coming, and a group of friends and I are getting ready for it :) We decided to build a compile-time Arbitrary precision Unsigned Integers. We would like to provide a set of integers algorithms(functions) with the library. We have seen a number of requests for such a library(SoC2010, C++0x Standard Library wishlist). Also, a regular run-time bigint is requested usually with that, but we don't want to go into the hassle of memory management. The idea came to me from a library called TTMath, unfortunately this library works only on specific platforms because Assembly was used extensively in the library. We would like to write a standard library, depending on the C++ standard library and Boost. Also, we would like to use the available C++0x facilities in current compilers like user-defined literals and others. This would technically make the library non-standard for a while, but we think that it is a matter of time the new standards will be official. Your hints on the whole process including design, implementation, documentation, maintainable of the library are more than welcom. We are a group of students and fresh graduates who are looking for something interesting in the summer, but we see that Boost is full of gurus and we don't want to forget something too obvious. We are communicating on-line, so there is no shared white-boards :( Thanks,

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• Algorithm to determine indices i..j of array A containing all the elements of another array B

  - by Skylark

  I came across this question on an interview questions thread. Here is the question: Given two integer arrays A [1..n] and B[1..m], find the smallest window in A that contains all elements of B. In other words, find a pair < i , j such that A[i..j] contains B[1..m]. If A doesn't contain all the elements of B, then i,j can be returned as -1. The integers in A need not be in the same order as they are in B. If there are more than one smallest window (different, but have the same size), then its enough to return one of them. Example: A[1,2,5,11,2,6,8,24,101,17,8] and B[5,2,11,8,17]. The algorithm should return i = 2 (index of 5 in A) and j = 9 (index of 17 in A). Now I can think of two variations. Let's suppose that B has duplicates. This variation doesn't consider the number of times each element occurs in B. It just checks for all the unique elements that occur in B and finds the smallest corresponding window in A that satisfies the above problem. For example, if A[1,2,4,5,7] and B[2,2,5], this variation doesn't bother about there being two 2's in B and just checks A for the unique integers in B namely 2 and 5 and hence returns i=1, j=3. This variation accounts for duplicates in B. If there are two 2's in B, then it expects to see at least two 2's in A as well. If not, it returns -1,-1. When you answer, please do let me know which variation you are answering. Pseudocode should do. Please mention space and time complexity if it is tricky to calculate it. Mention if your solution assumes array indices to start at 1 or 0 too. Thanks in advance.

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• How to alter Postgres table data based on its contents?

  - by williamjones

  This is probably a super simple question, but I'm struggling to come up with the right keywords to find it on Google. I have a Postgres table that has among its contents a column of type text named content_type. That stores what type of entry is stored in that row. There are only about 5 different types, and I decided I want to change one of them to display as something else in my application (I had been directly displaying these). It struck me that it's funny that my view is being dictated by my database model, and I decided I would convert the types being stored in my database as strings into integers, and enumerate the possible types in my application with constants that convert them into their display names. That way, if I ever got the urge to change any category names again, I could just change it with one alteration of a constant. I also have the hunch that storing integers might be somewhat more efficient than storing text in the database. First, a quick threshold question of, is this a good idea? Any feedback or anything I missed? Second, and my main question, what's the Postgres command I could enter to make an alteration like this? I'm thinking I could start by renaming the old content_type column to old_content_type and then creating a new integer column content_type. However, what command would look at a row's old_content_type and fill in the new content_type column based off of that?

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• WP7: Why does a ListBox.ItemsPanel break my ElementName data binding?

  - by iguanaNet

  I have a Windows Phone 7 ListBox that binds to a list of integers. I am using the default MVVM Light template, so there is a ViewModel class that contains data and a simple RelayCommand. Here is the ListBox: <ListBox ItemsSource="{Binding MyData}"> <ListBox.ItemTemplate> <DataTemplate> <Button Content="{Binding}"> <i:Interaction.Triggers> <i:EventTrigger EventName="Click"> <cmd:EventToCommand Command="{Binding ElementName=ContentGrid, Path=DataContext.TestCommand}" CommandParameter="{Binding}" /> </i:EventTrigger> </i:Interaction.Triggers> </Button> </DataTemplate> </ListBox.ItemTemplate> </ListBox> This displays a vertical list of integers inside buttons. If you click any of them, the following command code executes and shows a pop-up: new RelayCommand<int>(i => MessageBox.Show("Test" + i)); However, if I simply add the following XAML to change to a horizontal list, the databinding fails. Nothing happens when you click the button and no error messages are written to the Output window. <ListBox.ItemsPanel> <ItemsPanelTemplate> <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" /> </ItemsPanelTemplate> </ListBox.ItemsPanel> I have tried some other types of binding for the EventToCommand. For example, specifying my ViewModel as a static resource. It works, but is less ideal than the example above. Why does that ItemsPanel break the databinding?

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• Store a signed long int (32bit) as 4 octets?

  - by Doori Bar

  I managed to get a unsigned long int octets-representation (BE) by reading IPv4 methods, and I managed to read about how signed integers are using the MSB as the sign indicator, which makes 00 00 00 00 to be 0, while 7F FF FF FF is 2147483647. But I can't manage how to do the same for signed long integers? #include <stdio.h> #include <string.h> int main (void) { unsigned long int intu32; unsigned char octets[4]; intu32 = 255; octets[3] = (intu32) & 255; octets[2] = (intu32 >> 8) & 255; octets[1] = (intu32 >> 16) & 255; octets[0] = (intu32 >> 24) & 255; printf("(%d)(%d)(%d)(%d)\n", octets[0], octets[1], octets[2], octets[3]); intu32 = (octets[0] << 24) | (octets[1] << 16) | (octets[2] << 8) | octets[3]; printf("intu32:%lu\n", intu32); return 0; } Thanks in advance, Doori bar

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• Is False == 0 and True == 1 in Python an implementation detail or guaranteed by the language?

  - by EOL

  Is it guaranteed that False == 0 and True == 1, in Python? For instance, is it in any way guaranteed that the following code will always produce the same results, whatever the version of Python (existing and in the foreseeable future)? 0 == False # True 1 == True # True ['zero', 'one'][False] # is 'zero' Any reference to the official documentation would be much appreciated! Other comments would be appreciated too… :) Edit: As noted in many answers, bool inherits from int. The question can therefore be recast as: "Is this an implementation detail that might change in the future, or does the documentation officially say that programmers can rely on booleans inheriting from integers?". This question is relevant for writing robust code that won't fail because of implementation details! Edit 2: The original question is still open, I believe (even though I accepted what I thought was the closest answer): even though Python 3 officially recognizes booleans as integers, I have not yet seen any official integer values for False and True… It therefore looks to me like it is best to stay clear from the assumption that False==0 and True==1.

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• SQL Server 2008 Prior String Extract

  - by Saidur Rahman

  I have strings like the ones below in a SQL column. I want to extract them as a Gigabyte amount in aggregate. Example: Original Column ---------> Expected Output from a TSQL function ------------------------------------------- $15 / 1GB 24m + Intern 120MB ----------> 1.12 GB $19.95 / 500MB + $49.95 / 9GB Blackberry -----> 9.5GB $174.95 Blackberry 24GB + $10 / 1GB Datapack ----> 25GB $79 / 6GB --> 6GB Null --> Null $20 Plan --> 0GB Note: for our purpose, 1000MB = 1 GB (not 1024). The pattern is numbers followed by GB/MB, usually they are combined like 1GB (without any space but may sometimes may contain a space, it is not particularly important if hard to implement for this exception). Sometimes there are up to three or four instances of GB/MB occurring in the same string which are usually separated by a + sign (see row 2 and 3 of my example above). I have seen how we extract the dollar values in one of the answers where numbers were followed by $ or extract all integers in a string but I don't want to extract the dollar values or all the integers in a string. I just want the sum of GB/MB in the string.

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• How can we find second maximum from array efficiently?

  - by Xinus

  Is it possible to find the second maximum number from an array of integers by traversing the array only once? As an example, I have a array of five integers from which I want to find second maximum number. Here is an attempt I gave in the interview: #define MIN -1 int main() { int max=MIN,second_max=MIN; int arr[6]={0,1,2,3,4,5}; for(int i=0;i<5;i++){ cout<<"::"<<arr[i]; } for(int i=0;i<5;i++){ if(arr[i]>max){ second_max=max; max=arr[i]; } } cout<<endl<<"Second Max:"<<second_max; int i; cin>>i; return 0; } The interviewer, however, came up with the test case int arr[6]={5,4,3,2,1,0};, which prevents it from going to the if condition the second time. I said to the interviewer that the only way would be to parse the array two times (two for loops). Does anybody have a better solution?

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• C++ - my loop keeps on adding up to 0

  - by user1756913

  so far here's my code #include <iostream> using namespace std; int main () { int num1 = 0; int num2 = 0; int sum = 0; for(num2 = num1; num1 <= num2; num1 +=2) sum += num1; num1 = num1 / 2 == 0? num1 : num1 + 1; num2 = num2 / 2 == 0? num2 : num2 - 1; cout << "Enter the First Number:" << endl; cin >> num1; cout << "Enter the Second Number:" << endl; cin >> num2; cout << "Total Sum: " << sum << endl; } //end for but the sum keeps on adding up to 0 :/ here's the problem. Create a program that displays the sum of the even numbers between and including two numbers entered by the user. In other words, if the user enters an even number, that number should be included in the sum. For example, if the user enters the integers 2 and 7, the sum is 12 (2 + 4 + 6). If the user enters the integers 2 and 8, the sum is 20 (2 + 4 + 6 + 8 ). Display an error message if the first integer entered by the user is greater than the second integer.

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• Python: How to transfer varrying length arrays over a network connection

  - by Devin

  Hi, I need to transfer an array of varying length in which each element is a tuple of two integers. As an example: path = [(1,1),(1,2)] path = [(1,1),(1,2),(2,2)] I am trying to use pack and unpack, however, since the array is of varying length I don't know how to create a format such that both know the format. I was trying to turn it into a single string with delimiters, such as: msg = 1&1~1&2~ sendMsg = pack("s",msg) or sendMsg = pack("s",str(msg)) on the receiving side: path = unpack("s",msg) but that just prints 1 in this case. I was also trying to send 4 integers as well, which send and receive fine, so long as I don't include the extra string representing the path. sendMsg = pack("hhhh",p.direction[0],p.direction[1],p.id,p.health) on the receive side: x,y,id,health = unpack("hhhh",msg) The first was for illustration as I was trying to send the format "hhhhs", but either way the path doesn't come through properly. Thank-you for your help. I will also be looking at sending a 2D array of ints, but I can't seem to figure out how to send these more 'complex' structures across the network. Thank-you for your help.

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• LINQ Expression - Dynamic From & Where Clause

  - by chillydk147

  I have the following list of integers that I need to extract varying lists of integers containing numbers from say 2-4 numbers in count. The code below will extract lists with only 2 numbers. var numList = new List<int> { 5, 20, 1, 7, 19, 3, 15, 60, 3, 21, 57, 9 }; var selectedNums = (from n1 in numList from n2 in numList where (n1 > 10) && (n2 > 10) select new { n1, n2 }).ToList(); Is there any way to build up this Linq expression dynamically so that if I wanted lists of 3 numbers it would be compiled as below, this would save me having to package the similar expression inside a different method. var selectedNums = (from n1 in numList from n2 in numList from n3 in numList where (n1 > 10) && (n2 > 10) && (n3 > 10) select new { n1, n2, n3 }).ToList();

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• Explaining a Ruby code snippet

  - by Michael Foukarakis

  I'm in that uncomfortable position again, where somebody has left me with a code snippet in a language I don't know and I have to maintain it. While I haven't introduced Ruby to myself some parts of it are quite simple, but I'd like to hear your explanations nonetheless. Here goes: words = File.open("lengths.txt") {|f| f.read }.split # read all lines of a file in 'words'? values = Array.new(0) words.each { |value| values << value.to_i } # looked this one up, it's supposed to convert to an array of integers, right? values.sort! values.uniq! diffs = Array.new(0) # this looks unused, unless I'm missing something obvious sum = 0 s = 0 # another unused variable # this looks like it's computing the sum of differences between successive # elements, but that sum also remains unused, or does it? values.each_index { |index| if index.to_i < values.length-1 then sum += values.at(index.to_i + 1) - values.at(index.to_i) end } # could you also explain the syntax here? puts "delta has the value of\n" # this will eventually print the minimum of the original values divided by 2 puts values.at(0) / 2 The above script was supposed to figure out the average of the differences between every two successive elements (integers, essentially) in a list. Am I right in saying this is nowhere near what it actually does, or am I missing something fundamental, which is likely considering I have no Ruby knowledge?

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• Heapsort not working in Python for list of strings using heapq module

  - by VSN

  I was reading the python 2.7 documentation when I came across the heapq module. I was interested in the heapify() and the heappop() methods. So, I decided to write a simple heapsort program for integers: from heapq import heapify, heappop user_input = raw_input("Enter numbers to be sorted: ") data = map (int, user_input.split(",")) new_data = [] for i in range(len(data)): heapify(data) new_data.append(heappop(data)) print new_data This worked like a charm. To make it more interesting, I thought I would take away the integer conversion and leave it as a string. Logically, it should make no difference and the code should work as it did for integers: from heapq import heapify, heappop user_input = raw_input("Enter numbers to be sorted: ") data = user_input.split(",") new_data = [] for i in range(len(data)): heapify(data) print data new_data.append(heappop(data)) print new_data Note: I added a print statement in the for loop to see the heapified list. Here's the output when I ran the script: `$ python heapsort.py Enter numbers to be sorted: 4, 3, 1, 9, 6, 2 [' 1', ' 3', ' 2', ' 9', ' 6', '4'] [' 2', ' 3', '4', ' 9', ' 6'] [' 3', ' 6', '4', ' 9'] [' 6', ' 9', '4'] [' 9', '4'] ['4'] [' 1', ' 2', ' 3', ' 6', ' 9', '4']` The reasoning I applied was that since the strings are being compared, the tree should be the same if they were numbers. As is evident, the heapify didn't work correctly after the third iteration. Could someone help me figure out if I am missing something here? I'm running Python 2.4.5 on RedHat 3.4.6-9. Thanks, VSN

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• Why doesn't my processor have built-in BigInt support?

  - by ol

  As far as I understood it, BigInts are usually implemented in most programming languages as strings containing numbers, where, eg.: when adding two of them, each digit is added one after another like we know it from school, e.g.: 246 816 * * ---- 1062 Where * marks that there was an overflow. I learned it this way at school and all BigInt adding functions I've implemented work similar to the example above. So we all know that our processors can only natively manage ints from 0 to 2^32 / 2^64. That means that most scripting languages in order to be high-level and offer arithmetics with big integers, have to implement/use BigInt libraries that work with integers as strings like above. But of course this means that they'll be far slower than the processor. So what I've asked myself is: Why doesn't my processor have a built-in BigInt function? It would work like any other BigInt library, only (a lot) faster and at a lower level: Processor fetches one digit from the cache/RAM, adds it, and writes the result back again. Seems like a fine idea to me, so why isn't there something like that?

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