logical-operators

问题 I am not trying to solve any particular problem, but trying to learn R and understand its logical negation operator "!" documented on page http://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html It works for me when used in combination with =, in expressions such as: 1 != 2 TRUE But I can't quite comprehend standalone application of this operator. For instance, can I use it to select elements of the list which do not have specific name. Here's my attempt to do that, but it did not

问题 What is the difference between & and && in C? My teacher gave me this example: int a = 8; int b = 4; printf("a & b = %d\n", a & b); printf("a && b = %d\n", a && b); Output: a & b = 0; a && b = 1; I'm not sure why this would return true in one scenario and false in another. 回答1: & is bitwise and and && is logical and . The expression x && y will return 1 if both x and y is non-zero, and 0 otherwise. Note that if x is zero, then y will not be evaluated at all. The expression x & y will perform

问题 What is the difference between & and && in C? My teacher gave me this example: int a = 8; int b = 4; printf("a & b = %d\n", a & b); printf("a && b = %d\n", a && b); Output: a & b = 0; a && b = 1; I'm not sure why this would return true in one scenario and false in another. 回答1: & is bitwise and and && is logical and . The expression x && y will return 1 if both x and y is non-zero, and 0 otherwise. Note that if x is zero, then y will not be evaluated at all. The expression x & y will perform

问题 This question already has answers here : Why does the logical or operator (||) with an empty arrow function (()=>{}) cause a SyntaxError? (3 answers) Closed last year . The following code, when executed, true && () => {} yields Uncaught SyntaxError: Malformed arrow function parameter list Why ? Edit: I know wrapping the function in parenthesis works, thanks everyone, but I'd like to understand why can't the parser figure out it's a function in the first place. 回答1: The reason is due the first

问题 I need to create a logical variable (True-False) out of a categorical (factor) variable I decided to use the: dat$var[dat$var %in% c("option1")] <- TRUE dat$var[dat$var %in% c("option2")] <- FALSE But I get the following error message in both lines and my entire variable is NA: Warning message: In `[<-.factor`(`*tmp*`, dat$var %in% c("option1"), : invalid factor level, NA generated Any ideas on what I might be doing wrong? The factor level is right, I copy pasted to make sure there will not

问题 I need to create a logical variable (True-False) out of a categorical (factor) variable I decided to use the: dat$var[dat$var %in% c("option1")] <- TRUE dat$var[dat$var %in% c("option2")] <- FALSE But I get the following error message in both lines and my entire variable is NA: Warning message: In `[<-.factor`(`*tmp*`, dat$var %in% c("option1"), : invalid factor level, NA generated Any ideas on what I might be doing wrong? The factor level is right, I copy pasted to make sure there will not

问题 In this search query (test it live ↗) I'm searching for: all pull requests by user limonte (me) for the vaadin company How can I search for all my pull requests except (logical NOT) those for vaadin company? These two options I tried without success: is:pr author:limonte user:!vaadin is:pr author:limonte user:NOT vaadin 回答1: Prefixing any search qualifier with a - excludes all results that are matched by that qualifier. For example, you might be interested in finding all "cats" repositories

问题 In this search query (test it live ↗) I'm searching for: all pull requests by user limonte (me) for the vaadin company How can I search for all my pull requests except (logical NOT) those for vaadin company? These two options I tried without success: is:pr author:limonte user:!vaadin is:pr author:limonte user:NOT vaadin 回答1: Prefixing any search qualifier with a - excludes all results that are matched by that qualifier. For example, you might be interested in finding all "cats" repositories

问题 In C I want to check if variable equal to multiple values and I don't know how to code it without separating it fully. if (str[i]=='u'||'o'||'i'||'e'||'a') giving me always true and I don't understand why, I need explanation. if (str[i]==('u'||'o'||'i'||'e'||'a')) giving me always false and I don't understand why, I need explanation. thanks. 回答1: The reason why the following expression is always returning true: if (str[i] == 'u'||'o'||'i'||'e'||'a') is that character constants evaluate to

问题 I have two lists of zeros and ones. Both lists are of same length. The following is just an example, i am looking for a generic solution for lists of any sizes and with zeros and ones at any index. l1 = [1,1,0,1,1,1,1] l2 = [0,0,0,1,0,0,0] The goal is to use the first list l1 as mask to create a new list l2_new from l2 that logicaly OR merges all elements of indizes where l1 is 1 and adopts elements unchanged where l1 is 0 . Which would result to: l2_new = [0,0,1] Graphical explanation: 回答1: