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  • Idiomatic scheme and generic programming, why only on numbers ?

    - by Skeptic
    Hi, In Scheme, procedures like +, -, *, / works on different types of numbers, but we don't much see any other generic procedures. For example, length works only on list so that vector-length and string-length are needed. I guess it comes from the fact that the language doesn't really offer any mechanism for defining generic procedure (except cond of course) like "type classes" in Haskell or a standardized object system. Is there an idiomatic scheme way to handle generic procedures that I'm not aware of ?

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  • How would you program Pascal's triangle in R?

    - by Peter Flom
    I am reading, on my own (not for HW) about programming, and one exercise involved programming Pascal's triangle in R. My first idea was to make a list and then append things to it, but that didn't work too well. Then I thought of starting with a vector, and making a list out of that, at the end. Then I thought of making a matrix, and making a list out of that at the end. Not sure which way to even approach this. Any hints? thanks

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  • C++ STL containers

    - by cambr
    Different STL containers like vector, stack, set, queue, etc support different access methods on them. If you are coding for example in Notepad++ or vim, you have to continuously refer to the documentation to see what all methods are available, atleast I have to. Is there some good way of remembering which container supports which methods??

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  • Standard library function in R for finding the mode?

    - by Nick
    In statistical language R, mean() and median() are standard functions which do what you'd expect. mode() tells you the internal storage mode of the R object, not the value that occurs the most in its argument. But surely there is a standard library function that implements mode for a vector (or list).

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  • Help with code optimization

    - by Ockonal
    Hello, I've written a little particle system for my 2d-application. Here is raining code: // HPP ----------------------------------- struct Data { float x, y, x_speed, y_speed; int timeout; Data(); }; std::vector<Data> mData; bool mFirstTime; void processDrops(float windPower, int i); // CPP ----------------------------------- Data::Data() : x(rand()%ScreenResolutionX), y(0) , x_speed(0), y_speed(0), timeout(rand()%130) { } void Rain::processDrops(float windPower, int i) { int posX = rand() % mWindowWidth; mData[i].x = posX; mData[i].x_speed = WindPower*0.1; // WindPower is float mData[i].y_speed = Gravity*0.1; // Gravity is 9.8 * 19.2 // If that is first time, process drops randomly with window height if (mFirstTime) { mData[i].timeout = 0; mData[i].y = rand() % mWindowHeight; } else { mData[i].timeout = rand() % 130; mData[i].y = 0; } } void update(float windPower, float elapsed) { // If this is first time - create array with new Data structure objects if (mFirstTime) { for (int i=0; i < mMaxObjects; ++i) { mData.push_back(Data()); processDrops(windPower, i); } mFirstTime = false; } for (int i=0; i < mMaxObjects; i++) { // Sleep until uptime > 0 (To make drops fall with randomly timeout) if (mData[i].timeout > 0) { mData[i].timeout--; } else { // Find new x/y positions mData[i].x += mData[i].x_speed * elapsed; mData[i].y += mData[i].y_speed * elapsed; // Find new speeds mData[i].x_speed += windPower * elapsed; mData[i].y_speed += Gravity * elapsed; // Drawing here ... // If drop has been falled out of the screen if (mData[i].y > mWindowHeight) processDrops(windPower, i); } } } So the main idea is: I have some structure which consist of drop position, speed. I have a function for processing drops at some index in the vector-array. Now if that's first time of running I'm making array with max size and process it in cycle. But this code works slower that all another I have. Please, help me to optimize it. I tried to replace all int with uint16_t but I think it doesn't matter.

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  • Memory Allocation by STL C++ Objects

    - by Vaibhav
    I am using malloc_stats() function to display the amount of "system bytes" and "in use" bytes used by the process. I wanted to know if the in use bytes also include the memory used by STL C++ Objects like map, vector, sets? If yes, is it safe to assume that this is only amount of memory that will be used by the process?

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  • Create lags with a for-loop in R

    - by cptn
    I've got a data.frame with stock data of several companies (here it's only two). I want 10 additional columns in my stock data.frame df with lagged dates (from -5 days to +5 days) for both companies in my event data.frame. I'm using a for loop which is probably not the best solution, but it works partially. DATE <- c("01.01.2000","02.01.2000","03.01.2000","06.01.2000","07.01.2000","09.01.2000","10.01.2000","01.01.2000","02.01.2000","04.01.2000","06.01.2000","07.01.2000","09.01.2000","10.01.2000") RET <- c(-2.0,1.1,3,1.4,-0.2, 0.6, 0.1, -0.21, -1.2, 0.9, 0.3, -0.1,0.3,-0.12) COMP <- c("A","A","A","A","A","A","A","B","B","B","B","B","B","B") df <- data.frame(DATE, RET, COMP, stringsAsFactors=F) df # DATE RET COMP # 1 01.01.2000 -2.00 A # 2 02.01.2000 1.10 A # 3 03.01.2000 3.00 A # 4 06.01.2000 1.40 A # 5 07.01.2000 -0.20 A # 6 09.01.2000 0.60 A # 7 10.01.2000 0.10 A # 8 01.01.2000 -0.21 B # 9 02.01.2000 -1.20 B # 10 04.01.2000 0.90 B # 11 06.01.2000 0.30 B # 12 07.01.2000 -0.10 B # 13 09.01.2000 0.30 B # 14 10.01.2000 -0.12 B this loop works fine comp <- as.vector(unique(df$COMP)) mylist <- vector('list', length(comp)) # create lags in DATE for(i in 1:length(comp)) { print(i) comp_i <- comp[i] df_k <- df[df$COMP %in% comp_i, ] # all trading days of one firm df_k <- transform(df_k, DATEm1 = c(NA, head(DATE, -1)), DATEm2 = c(NA, NA, head(DATE, -2)), DATEm3 = c(NA, NA, NA, head(DATE, -3)), DATEm4 = c(NA, NA, NA, NA,head(DATE, -4)), DATEm5 = c(NA, NA, NA, NA, NA, head(DATE, -5)), DATEp1 = c(DATE[-1], NA)) #DATEp2 = c(DATE[-2], NA, NA), #DATEp3 = c(DATE[-3], NA, NA, NA), #DATEp4 = c(DATE[-4], NA, NA, NA, NA), #DATEp5 = c(DATE[-5], NA, NA, NA, NA, NA)) mylist[[i]] = df_k } df1 <- do.call(rbind, mylist) But if I add the lines with DATEp2, DATEp3, DATEp4, DATEp5. the code doesn't work. Can anybody tell me what I'm doing wrong here? Here the code with all the lagged dates. # create lags in DATE for(i in 1:length(comp)) { print(i) comp_i <- comp[i] df_k <- df[df$COMP %in% comp_i, ] # all trading days of one firm df_k <- transform(df_k, DATEm1 = c(NA, head(DATE, -1)), DATEm2 = c(NA, NA, head(DATE, -2)), DATEm3 = c(NA, NA, NA, head(DATE, -3)), DATEm4 = c(NA, NA, NA, NA,head(DATE, -4)), DATEm5 = c(NA, NA, NA, NA, NA, head(DATE, -5)), DATEp1 = c(DATE[-1], NA), DATEp2 = c(DATE[-2], NA, NA), DATEp3 = c(DATE[-3], NA, NA, NA), DATEp4 = c(DATE[-4], NA, NA, NA, NA), DATEp5 = c(DATE[-5], NA, NA, NA, NA, NA)) mylist[[i]] = df_k } df1 <- do.call(rbind, mylist)

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  • Copying from istream never stops

    - by the_drow
    This bit of code runs infinitely: copy(istream_iterator<char>(cin), istream_iterator<char>(), back_inserter(buff)); The behavior I was expecting is that it will stop when I press enter. However it doesn't. buff is a vector of chars.

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  • Refactor the following two C++ methods to move out duplicate code

    - by ossandcad
    I have the following two methods that (as you can see) are similar in most of its statements except for one (see below for details) unsigned int CSWX::getLineParameters(const SURFACE & surface, vector<double> & params) { VARIANT varParams; surface->getPlaneParams(varParams); // this is the line of code that is different SafeDoubleArray sdParams(varParams); for( int i = 0 ; i < sdParams.getSize() ; ++i ) { params.push_back(sdParams[i]); } if( params.size() > 0 ) return 0; return 1; } unsigned int CSWX::getPlaneParameters(const CURVE & curve, vector<double> & params) { VARIANT varParams; curve->get_LineParams(varParams); // this is the line of code that is different SafeDoubleArray sdParams(varParams); for( int i = 0 ; i < sdParams.getSize() ; ++i ) { params.push_back(sdParams[i]); } if( params.size() > 0 ) return 0; return 1; } Is there any technique that I can use to move the common lines of code of the two methods out to a separate method, that could be called from the two variations - OR - possibly combine the two methods to a single method? The following are the restrictions: The classes SURFACE and CURVE are from 3rd party libraries and hence unmodifiable. (If it helps they are both derived from IDispatch) There are even more similar classes (e.g. FACE) that could fit into this "template" (not C++ template, just the flow of lines of code) I know the following could (possibly?) be implemented as solutions but am really hoping there is a better solution: I could add a 3rd parameter to the 2 methods - e.g. an enum - that identifies the 1st parameter (e.g. enum::input_type_surface, enum::input_type_curve) I could pass in an IDispatch and try dynamic_cast< and test which cast is NON_NULL and do an if-else to call the right method (e.g. getPlaneParams() vs. get_LineParams()) The following is not a restriction but would be a requirement because of my teammates resistance: Not implement a new class that inherits from SURFACE/CURVE etc. (They would much prefer to solve it using the enum solution I stated above)

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  • Difference between a Deprecated and Legacy API?

    - by Vaibhav Bajpai
    I was studying the legacy API's in the Java's Collection Framework and I learnt that classes such as Vector and HashTable have been superseded by ArrayList and HashMap. However still they are NOT deprecated, and deemed as legacy when essentially, deprecation is applied to software features that are superseded and should be avoided, so, I am not sure when is a API deemed legacy and when it is deprecated.

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  • Determining if two lines intersect

    - by Faken
    I have two lines that extend to infinity but both have a starting point. They are both described by a starting point and a vector in the direction of the line extending to infinity. I want to find out if the two lines intersect but i don't need to know where they intersect (its part of a collision detection algorithm). Everything i have looked at so far describes finding the intersection point of two lines or line segments. Anyone know a fast algorithm to solve this?

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  • Create a dataset: extract features from text documents (TF-IDF)

    - by BigG
    I've to create a dataset from some text files, writing them as vectors of features. Something like this: doc1: 1,0.45 6,0.001 94,0.1 ... doc2: 3,0.5 98,0.2 ... ... each position of the vector represent a word, and the score is given by something like TF-IDF. Do you know some library/tool/whatever for this? (java is better)

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  • Android Speed based on accelerometer values

    - by fraguas
    Hi. I need to obtain the velocity of an android device, based on the accelerometer values. I made a code that allows me to get the accelerometer values, and then I calculate the velocity, using the formula: v = v0 + at. (vector calculation) My problem is that my velocity only increases and never decreases. I think the problem is that the device never gets an negative acceleration. Can you help me with this?

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  • Long numbers. Division.

    - by user577395
    Hello, world! I have a problem. Today I tried to create a code, which finds Catalan number. But in my program can be long numbers. I found numerator and denominator. But i can't div long numbers! Also, only standard libraries was must use in this program. Help me please. This is my code #include <vector> #include <iostream> using namespace std; int main(int argc, char *argv[]) { const int base = 1000*1000*1000; vector <int> a, b; int n, carry = 0; cin>>n; a.push_back(n); for (int ii=n+2; ii!=(2*n)+1;++ii) { carry = 0; for (size_t i=0; i<a.size() || carry; ++i) { if (i == a.size()) a.push_back (0); long long cur = carry + a[i] * 1ll * ii; a[i] = int (cur % base); carry = int (cur / base); } } while (a.size() > 1 && a.back() == 0) a.pop_back(); b.push_back(n); for (int ii=1; ii!=n+1;++ii) { carry = 0; for (size_t i=0; i<b.size() || carry; ++i) { if (i == b.size()) b.push_back (0); long long cur = carry + b[i] * 1ll * ii; b[i] = int (cur % base); carry = int (cur / base); } } while (b.size() > 1 && b.back() == 0) b.pop_back(); cout<<(a.empty() ? 0 : a.back()); for (int i=(int)a.size()-2; i>=0; --i) cout<<(a[i]); cout<<" "; cout<<(b.empty() ? 0 : b.back()); for (int i=(int)b.size()-2; i>=0; --i) cout<<(b[i]); //system("PAUSE"); cout<<endl; return 0; } P.S. Sorry for my bad english =)

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  • C++ parent class alignment

    - by aaa
    hello. Is it possible to specify alignment of parent class? for example something like (which does not compiled): template<size_t n> class Vector : public boost::array<double,n> __attribute__ ((aligned(16))) { thanks

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  • Indexing one-dimensional numpy.array as matrix

    - by Alain
    I am trying to index a numpy.array with varying dimensions during runtime. To retrieve e.g. the first row of a n*m array a, you can simply do a[0,:] However, in case a happens to be a 1xn vector, this code above returns an index error: IndexError: too many indices As the code needs to be executed as efficiently as possible I don't want to introduce an if statement. Does anybody have a convenient solution that ideally doesn't involve changing any data structure types?

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