Ruby 中的“upto”方法

The 'upto' method in Ruby

提问by Billjk

I'm learning Ruby, and there has been a bit of talk about the uptomethod in the book from which I am learning. I'm confused. What exactly does it do?

我正在学习 Ruby，并且在我学习upto的书中有一些关于方法的讨论。我糊涂了。它究竟有什么作用？

Example:

例子：

grades = [88,99,73,56,87,64]
sum = 0
0.upto(grades.length - 1) do |loop_index|
    sum += grades[loop_index]
end
average = sum/grades.length
puts average

回答by knut

Let's try an explanation:

让我们尝试一个解释：

You define an array

你定义一个数组

grades = [88,99,73,56,87,64]

and prepare a variable to store the sum:

并准备一个变量来存储总和：

sum = 0

grades.lengthis 6 (there are 6 elements in the array), (grades.length - 1)is 5.

grades.length是 6（数组中有 6 个元素），(grades.length - 1)是 5。

with 0.upto(5)you loop from 0 to 5, loop_indexwill be 0, then 1...

随着0.upto(5)你从 0 到 5 循环，loop_index将是 0，然后是 1...

The first element of the array is grades[0](the index in the array starts with 0). That's why you have to subtract 1 from the number of elements.

数组的第一个元素是grades[0]（数组中的索引从 0 开始）。这就是为什么你必须从元素数中减去 1。

0.upto(grades.length - 1) do |loop_index|

Add the loop_index's value to sum.

将 loop_index 的值添加到 sum。

    sum += grades[loop_index]
end

Now you looped on each element and have the sum of all elements of the array.

现在您循环了每个元素并获得了数组所有元素的总和。

You can calculate the average:

您可以计算平均值：

average = sum/grades.length

Now you write the result to stdout:

现在您将结果写入标准输出：

puts average

---

---

This was a non-ruby-likesyntax. Ruby-like you would do it like this:

这是一种非 ruby​​ 式语法。像 Ruby 一样，你会这样做：

grades = [88,99,73,56,87,64]
sum = 0
grades.each do |value|
    sum += value
end
average = sum/grades.length
puts average

---

---

Addendum based on Marc-Andrés comment:

基于 Marc-Andrés 评论的附录：

You may use also injectto avoid to define the initial sum:

您也可以使用inject来避免定义初始总和：

grades = [88,99,73,56,87,64] 
sum = grades.inject do |sum, value|     
  sum + value 
end
average = sum / grades.length 
puts average 

Or even shorter:

或者更短：

grades = [88,99,73,56,87,64] 
average = grades.inject(:+) / grades.length 
puts average 

回答by Oliver Charlesworth

From http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref_c_integer.html#upto:

从http://www.ruby-doc.org/docs/ProgrammingRuby/html/ref_c_integer.html#upto：

uptoint.upto( anInteger ) {| i | block }

Iterates block, passing in integer values from intup to and including anInteger.

5.upto(10) { |i| print i, " " }

produces:

5 6 7 8 9 10

取决于int.upto( anInteger ) {| i | block }

迭代block，传递从intup 到 并包括 的整数值anInteger。

5.upto(10) { |i| print i, " " }

产生：

5 6 7 8 9 10

回答by teleolurian

Upto executes the block given once for each number from the original number "upto" the argument passed. For example:

Upto 为从原始数字“直到”传递的参数的每个数字执行一次给定的块。例如：

1.upto(10) {|x| puts x}

will print out the numbers 1 through 10.

将打印出数字 1 到 10。

回答by ScottJShea

It is just another way to do a loop/iteratorin Ruby. It says do this action ntimes based on i being the first number the the number in parens as the limit.

这只是在 Ruby 中执行循环/迭代器的另一种方式。它说根据 i 是第一个数字执行此操作n次，以括号中的数字为限制。

回答by jndaigle

An alternative that looks more like Ruby to me is

对我来说看起来更像 Ruby 的另一种选择是

require 'descriptive_statistics'

grades=[88,99,73,56,87,64]
sum = grades.sum
average = grades.mean
sd = grades.standard_deviation

Of course it depends what you're doing.

当然，这取决于你在做什么。

回答by Chris Pettitt

My example would have been this:

我的例子是这样的：

1.upto(5)  { |i| puts "Countup: #{i}" }

So what you're actually doing here is saying, I want to count up from 1 to the number 5, that's specifically what this part is saying:

所以你在这里实际上是在说，我想从 1 数到数字 5，这就是这部分所说的：

1.upto(5)

The latter part of code (a block) is just outputting the iteration of going through the count from 1 up to 5. This is the output you might expect to see:

代码的后半部分（一个块）只是输出从 1 到 5 计数的迭代。这是您可能希望看到的输出：

    Countup: 1
    Countup: 2
    Countup: 3
    Countup: 4
    Countup: 5

Note: This can be written is another way if you're using multilines:

注意：如果您使用多行，可以用另一种方式编写：

1.upto(5) do |i|
puts "Countup: #{i}"
end

Hope this helps.

希望这可以帮助。