syntactic-sugar

问题 Lists or numpy arrays can be unpacked to multiple variables if the dimensions match. For a 3xN array, the following will work: import numpy as np a,b = [[1,2,3],[4,5,6]] a,b = np.array([[1,2,3],[4,5,6]]) # result: a=[1,2,3], b=[4,5,6] How can I achieve a similar behaviour for the columns of a pandas DataFrame ? Extending the above example: import pandas as pd df = pd.DataFrame([[1,2,3],[4,5,6]]) df.columns = ['A','B','C'] # Rename cols and df.index = ['i', 'ii'] # rows for clarity The

问题 I have been trying to get the rank of a vector in c++ using Rcpp. I have used other sugar functions like is_na(); Is there a similar sugar function for rank R function in c++. Also is there any list of available R sugar functions in Rcpp/ 回答1: 1) There is an order function here and order(order(x)) is rank(x, ties = "first") . 2) A second way would be: match(x, sort(x)) ADDED Second approach. 来源： https://stackoverflow.com/questions/23606266/rcpp-sugar-for-rank-function

问题 In McBride and Paterson's 'Applicative programming with effects' they introduce some lovely syntactic sugar for lifting a pure function: [| f x y z |] for f <$> x <*> y <*> z and I recall someone somewhere else using li f w x y z il or il f v w x y z li , and I thought/hoped that might be because it could be defined using some existing language feature and cunning definition of li and il . I can't find any reference to this beyond the paper, and assuming that [| and |] aren't likely to turn

问题 This question already has answers here : Understanding slice notation (32 answers) Closed 6 years ago . The extended slice syntax in python has been explained to me as " a[n:m:k] returns every kth element from n to m ". This gives me a good idea what to expect when k is positive. But I'm lost on how to interpret a[n:m:k] for negative k. I know that a[::-1] reverses a, and that a[::-k] takes ever kth element of the reversed a. But how is this a generalization of the definition for k positive?

问题 Note: I've seen this question asked sometimes before (a, b, c), but neither of these was in C#, nor helpful. Assume I'm using the ? : ternary operator like this (to do nothing when false is the case): r==5? r=0 : <nothing> ; I'm getting an error. Putting something there will obviously solve the problem. How can I still keep the other side empty without making some random empty function? 回答1: You can't. The whole point of the conditional ?: operator is that it evaluates an expression . You can

问题 From this post, I was told that the following section of code suffered from "the egregious act of closing over the loop variable." foreach (Canidate canidate in allCanidates) { Thread newThread = new Thread(delegate() { BusyWait(canidate); }); newThread.Start(); } I switched it to this: foreach (Canidate canidate in allCanidates) { var can = canidate; Thread newThread = new Thread(delegate() { BusyWait(can); }); newThread.Start(); } But my boss keeps insisting that it will suffer from the

问题 I just noticed this construct somewhere on web: val list = List(someCollection: _*) What does _* mean? Is this a syntax sugar for some method call? What constraints should my custom class satisfy so that it can take advantage of this syntax sugar? 回答1: Generally, the : notation is used for type ascription, forcing the compiler to see a value as some particular type. This is not quite the same as casting. val b = 1 : Byte val f = 1 : Float val d = 1 : Double In this case, you're ascribing the

问题 Does anyone know how to get the (Scala part only) desugared translation of a for/comprehension expression before it actually tries to compile in the REPL (or compiler)? The only thing I've found so far is the compiler "-print" flag but that gives you the full Scala translation… 回答1: As I already said in the other topic, scalac -print prints out scala code, not java. It translates all scala keywords that are not directly compatible with java to normal scala code. It is not possible to let the

问题 Does anyone know how to get the (Scala part only) desugared translation of a for/comprehension expression before it actually tries to compile in the REPL (or compiler)? The only thing I've found so far is the compiler "-print" flag but that gives you the full Scala translation… 回答1: As I already said in the other topic, scalac -print prints out scala code, not java. It translates all scala keywords that are not directly compatible with java to normal scala code. It is not possible to let the

问题 Here is my code. I want to write the expression 7? & 10? so that it compiles. object Test { trait A { def &(other: A) = ??? } case class B(i: Int) extends A implicit class C(i: Int) { def ? : A= B(i) } val u = 7? val v = 10? val w = u & v // Ok, it compiles val z = 7? & 10? //';' expected but 10 found val g = 7.? & 10? //';' expected but 10 found val h = (7?) & 10? //Type mismatch. found Int(10). Required Test.A val i = 7? & (10?) //Test.A does not take parameters (on the ?) } Why can't I