logical-operators

I am trying to save the data from a loop of logical tests. So I have the following data: T1 <- matrix(seq(from=100000, to=6600000,length.out=676),26,26) # a matrix of 26X26 - here with illustrive values minmax <- seq(from=1,to=49,by=1) # creates a sequence Fstep <- 6569141.82/minmax # define a vector from 0 to 6569141.82 with 49 divisions F <- rev(round(Fstep,0)) # round the vector values and re order them F I have runned the following loop for (i in 1:49) { print(T1 > F[i]) # I used print to see the results in the screen } This loop returns me 49 matrices filled in with logical values (True

I have given a list of indices, e.g. i = [3 5] and a vector v = 1:6 . I need a function f which returns the logical map for the vector v given the indices i , e.g.: f(i, length(v)) = [0 0 1 0 1 0] Since I will call this function several million times, I would like to make it as fast as possible. Is there a builtin function which performs this task? I know I'm late in the game, but I really wanted to find a faster solution which is just as elegant as ismember . And indeed there is one, that employs the undocumented ismembc function: ismembc(v, i) Benchmark N = 7; i = [3 5]; %// slayton's

Why does the first line return TRUE, and the third line returns 1? I would expect both lines to return 1. What is the exact meaning of those extra two parentheses in the third line? !is.na(5) + !is.na(NA) # TRUE (!is.na(5)) + (!is.na(NA)) # 1 edit: should check these multiple times. The original problem was with !is.na() , thought it replicated for is.na() . But it didn't :) ! has a weird, counter-intuitive precedence in R. Your first code is equivalent to !(is.na(5) + !is.na(NA)) That is, ! has lower precedence than + . 来源： https://stackoverflow.com/questions/17651687/behavior-of-summing-is

Quick question here about short-circuiting statements in C#. With an if statement like this: if (MyObject.MyArray.Count == 0 || MyObject.MyArray[0].SomeValue == 0) { //.... } Is it guaranteed that evaluation will stop after the "MyArray.Count" portion, provided that portion is true? Otherwise I'll get a null exception in the second part. Yes, this is guaranteed. C# Language Specification - 7.11 Conditional logical operators : The && and || operators are called the conditional logical operators. They are also called the "short-circuiting" logical operators. Therefore they will support logical

I assume this just returns an int. Is there anything else going on I should be aware of? C/C++ differences? float a = 2.5; !a; // What does this return? Int? Float? Regarding C++, quoting C++11 §5.3.1/9: The operand of the logical negation operator ! is contextually converted to bool ; its value is true if the converted operand is false and false otherwise. The type of the result is bool . So what's really relevant here is the behavior of static_cast<bool>(some_float) – quoting §4.12/1: A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a

I searched the site but did not find the answer I was looking for so here is a really quick question. I am trying to do something like that : #ifdef _WIN32 || _WIN64 #include <conio.h> #endif How can I do such a thing? I know that _WIN32 is defined for both 32 and 64 bit windows so I would be okay with either for windows detection. I am more interested in whether I can use logical operators like that with preprocessor directives, and if yes how, since the above does not work. Compiling with gcc I get : warning: extra tokens at end of #ifdef directive , and it basically just takes the first