variance

问题 How can I, in R calculate the overall variance and the variance for each group from a dataset that looks like this (for example): Group Count Value A 3 5 A 2 8 B 1 11 B 3 15 I know to calculate the variance as a whole, ignoring the groups I would do: var(rep(x$Value, x$Count)), but how do I automatically calculate the variance for each group accounting for the frequency? E.g., the variance for group A, group B, etc.,.. I would like my output to have the following headers: Group, Total Count,

问题 If I have a list like this: results=[-14.82381293, -0.29423447, -13.56067979, -1.6288903, -0.31632439, 0.53459687, -1.34069996, -1.61042692, -4.03220519, -0.24332097] I want to calculate the variance of this list in Python which is the average of the squared differences from the mean. How can I go about this? Accessing the elements in the list to do the computations is confusing me for getting the square differences. 回答1: You can use numpy's built-in function var: import numpy as np results =

问题 I wrote a program which looks up data in a separate txt file and then gives the average and the standard deviation. It finds my average but I get an error for Standard deviation. Was wondering anyone could help me fix my code. This is it: data = File.open("avg_temp.txt", "r+") contents = data.read contents = contents.split("\r\n") #split up array contents.collect! do |x| x.split(',') end sum = 0 contents.each do |x| #make loop to find average sum = sum + x[1].to_f end avg = sum / contents

问题 I've looked through a couple of other questions similar to mine, and the one most relevant wasn't answered, while the others all came down to missing data and data lengths. I am trying to model compositional dissmiliarity after a disturbance through time. I sampled at discrete timepoints: 0, 3, 6, and 9 months. I am interested in the fixed effect of time on recovery, but at each point, season and other environmental variables changed and led to differing variability between 0, 3, 6, and 9

问题 Can I have a type (for now forgetting its semantics) that can be covariant as well as contravariant? for example: public interface Foo<in out T> { void DoFooWith(T arg); } Off to Eric Lippert's blog for the meat and potatoes of variance in C# 4.0 as there's little else anywhere that covers adequate ground on the subject. I tried it out anyway, not only does it not allow that, but it tells me I am missing the whole point. I need to understand the link between read-only, write-only and variance

问题 Below is the code I am trying to run: class Student { def printDetails = println("I am a student") def printSomeOtherDetails = println("I love Studying") } class ComputerScienceStudent extends Student { override def printDetails = println("I am a Computer Science Student") override def printSomeOtherDetails = println("I love Scala") } class InformationTechnologyStudent extends Student { override def printDetails = println("I am an Information Technology Student") override def

问题 I'm having a little problem understanding variance of methods when overloading. While this perfectly works due to covariance in the return type class Bla class Fasel extends Bla trait Test[A] { def tester(): Bla = new Bla } class FooTest[A](a: A) extends Test[A] { override def tester(): Fasel = new Fasel } this one fails even though functions are contravariant in their parameter types. class Bla class Fasel extends Bla trait Test[A] { def tester(a: Fasel): Bla = new Bla } class FooTest[A](a:

问题 Suppose I'm using the typeclass pattern in Scala. Here's how I make a class C part of the typeclass Foo: Welcome to Scala version 2.9.0.1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_26). scala> trait Foo[T] { def foo(t: T) } defined trait Foo scala> def foo[T : Foo](t: T) { implicitly[Foo[T]].foo(t) } foo: [T](t: T)(implicit evidence$1: Foo[T])Unit scala> class C defined class C scala> foo(new C) <console>:11: error: could not find implicit value for evidence parameter of type Foo[C] foo

问题 I wanted to create an observableCollection that is sortable so i started creating a class that inherit observable with some methods to sort it, then i wanted that class to persist the index into the childs, so i created an interface that expose an index property where i can write to, and i costrainted the T of my collection class to be of my Interface, then i wanted to be able from avery item to access the parentCollection and here the problems started because the type of the parent

问题 I wanted to create an observableCollection that is sortable so i started creating a class that inherit observable with some methods to sort it, then i wanted that class to persist the index into the childs, so i created an interface that expose an index property where i can write to, and i costrainted the T of my collection class to be of my Interface, then i wanted to be able from avery item to access the parentCollection and here the problems started because the type of the parent