logical-operators | 易学教程

Element-wise logical OR in Pandas

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问题 I would like the element-wise logical OR operator. I know \"or\" itself is not what I am looking for. I am aware that AND corresponds to & and NOT, ~ . But what about OR? 回答1: The corresponding operator is | : df[(df < 3) | (df == 5)] would elementwise check if value is less than 3 or equal to 5. If you need a function to do this, we have np.logical_or. For two conditions, you can use df[np.logical_or(df<3, df==5)] Or, for multiple conditions use the logical_or.reduce , df[np.logical_or

What is the difference between logical and conditional AND, OR in C#? [duplicate]

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问题 This question already has answers here : Closed 9 years ago . Possible Duplicate: What is the diffference between the | and || or operators? Logical AND and OR: (x & y) (x | y) Conditional AND and OR: (x && y) (x || y) I\'ve only known about conditional operands up to this point. I know what it does and how to apply it in if-statements. But what is the purpose of logical operands? 回答1: I prefer to think of it as "bitwise vs. conditional" rather than "logical vs conditional" since the general

Logical operators in JavaScript — how do you use them?

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I don't understand how && , || , and ! work... both with bools and other data types. How do you use them? SLaks All values in Javascript are either "truthy" or "falsy". a && b evaluates to the first falsy operand a || b evaluates to the first truthy operand Both operators will not evaluate any operands after the one the return. If all operands don't match, it will evaluate to the last one. !a evaluates to true if a is falsy and false if a is truthy. All values are truthy except the following, which are falsy : false +0 -0 NaN "" null undefined document.all If you want to test that both of two

Why is there no logical xor in JavaScript?

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问题 Why is there no logical xor in JavaScript? 回答1: JavaScript traces its ancestry back to C, and C does not have a logical XOR operator. Mainly because it's not useful. Bitwise XOR is extremely useful, but in all my years of programming I have never needed a logical XOR. If you have two boolean variables you can mimic XOR with: if (a != b) With two arbitrary variables you could use ! to coerce them to boolean values and then use the same trick: if (!a != !b) That's pretty obscure though and

Why isn't “k” incremented in the statement “m = ++i && ++j || ++k” when “++i&&++j” evaluates to true? [duplicate]

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问题 This question already has an answer here: Short circuit behavior of logical expressions in C in this example 1 answer Aren\'t the individual expressions in a composite logical AND/OR expression supposed to be evaluated first before the logical operators are applied to their result?Why is ++k untouched in the condition m = ++i && ++j || ++k for the following program : #include<stdio.h> int main() { int i=-3, j=2, k=0, m; m = ++i && ++j || ++k; printf(\"%d, %d, %d, %d\\n\", i, j, k, m); return

Short-circuit evaluation on C

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问题 I\'m studying C from A Book on C by Kelley-Pohl, and there\'s this exercise that I don\'t understand: int a = 0, b = 0, x; x = 0 && (a = b = 777); printf(\"%d %d %d\\n\", a, b, x); x = 777 || (a = ++b); printf(\"%d %d %d\\n\", a, b, x); They just say to imagine the output and compare it to the real one. I thought the output would have been 777 777 0 778 778 1 but it is 0 0 0 0 0 1 回答1: The && operator uses lazy evaluation. If either side of the && operator is false , then the whole expression

CSS3 combining selectors with OR instead of AND

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问题 Given this selector: body[class*=\"page-node-add-\"][class~=\"page-node-edit\"] {background:red;} It will match a body which has a class that contains a substring of page-node-add- AND a class which is exactly page-node-edit I would like to say match the first OR the second (but not both). Is it possible? The problem with using a comma: If I have a long selector like: body[class*=\"page-node-add-\"] form.node-form > .field-type-field-collection > table > thead tr th, body[class~=\"page-node

Logical operators (“and”, “or”) in DOS batch

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How would you implement logical operators in DOS Batch files? You can do and with nested conditions: if %age% geq 2 ( if %age% leq 12 ( set class=child ) ) or: if %age% geq 2 if %age% leq 12 set class=child You can do or with a separate variable: set res=F if %hour% leq 6 set res=T if %hour% geq 22 set res=T if "%res%"=="T" ( set state=asleep ) The IF statement does not support logical operators ( AND and OR ), cascading IF statements make an implicit conjunction. IF Exist File1.Dat IF Exist File2.Dat GOTO FILE12_EXIST_LABEL If File1.Dat and File1.Dat exist then jump the label FILE12_EXIST

Logical operators (AND, OR) with NA, TRUE and FALSE

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问题 I cannot understand the properties of logical (boolean) values TRUE , FALSE and NA when used with logical OR ( | ) and logical AND ( & ). Here are some examples: NA | TRUE # [1] TRUE NA | FALSE # [1] NA NA & TRUE # [1] NA NA & FALSE # [1] FALSE Can you explain these outputs? 回答1: To quote from ?Logic : NA is a valid logical object. Where a component of x or y is NA, the result will be NA if the outcome is ambiguous. In other words NA & TRUE evaluates to NA, but NA & FALSE evaluates to FALSE.

Is there actually a reason why overloaded && and || don't short circuit?

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问题 The short circuiting behaviour of the operators && and || is an amazing tool for programmers. But why do they lose this behaviour when overloaded? I understand that operators are merely syntactic sugar for functions but the operators for bool have this behaviour, why should it be restricted to this single type? Is there any technical reasoning behind this? 回答1: All design processes result in compromises between mutually incompatible goals. Unfortunately, the design process for the overloaded