对于R中的“循环不一致” [英] 'For' loop inconsistencies in R

问题描述

虽然这不是一个好的做法，但我正在使用double for循环来执行计算。为了说明我得到的错误，下面的for循环会做。为什么j计数器在内循环中超过5？

 > （i（i，j））
 +} 
 [1（5）） ] 1 2 
 [1] 1 3 
 [1] 1 4 
 [1] 1 5 
 [1] 1 6 
 [1] 2 3 
 [1] 2 4 
 [1] 2 5 
 [1] 2 6 
 [1] 2 7 
 [1] 3 4 
 [1] 3 5 
 [1] 3 6 
 [1] 3 7 
 [1] 3 8 
 [1] 4 5 
 [1] 4 6 
 [1] 4 7 
 [1] 4 8 
 [1] 4 9 
 [1] 5 6 
 [1] 5 7 
 [1] 5 8 
 [1] 5 9 
 [1] 5 10 
  

解决

为什么j内部计数器在内循环中超过了'5'？

$ b （i + 1：5）中的（j在i + 1：5中）相当于 code>，它可以转化为（j在（i + 1）:( i + 5））中的元素



原因可以在这里找到



 定义了下面的一元和二元运算符。它们按照从高到低的顺序排列。 
 
 :: :::访问命名空间中的变量
 $ @组件/槽提取
 [[[indexing 
 ^幂（右至左）
  -  +一元减号和加号
：序列运算符### 
％任何特殊运算符（包括%%和％/％）
 * /乘除法
 + （binary）add，subtract ### 
  

##给我们这里感兴趣的操作符，序列比二进制add 更高的优先级，所以添加 i 如果你希望保持在（i + 1）的范围内：5


/ code>你必须照顾一个特殊情况，其中 i 是 5 成为 6：5 。

最后你的代码可以是：

pre $ for（i in 1：5）{
s < - min（i + 1,5）＃Per Ben Bolker comment
for（j在s：5）{
print（c（i，j））
}
}


输出：

  [1] 1 2 
 [1] 1 3 
 [1] 1 4 
 [1] 1 5 
 [ 1] 2 3 
 [1] 2 4 
 [1] 2 5 
 [1] 3 4 
 [1] 3 5 
 [1] 4 5 
 [1] 5 5 
  

Although it is not a good practice, I am using a double for loop to perform a calculation. To illustrate the error I am getting, the following for loop would do. Why is the 'j' counter exceeding '5' in the inner for loop?

> for(i in 1:5){
+   for(j in i+1:5)
+     print(c(i,j))
+ }
[1] 1 2
[1] 1 3
[1] 1 4
[1] 1 5
[1] 1 6
[1] 2 3
[1] 2 4
[1] 2 5
[1] 2 6
[1] 2 7
[1] 3 4
[1] 3 5
[1] 3 6
[1] 3 7
[1] 3 8
[1] 4 5
[1] 4 6
[1] 4 7
[1] 4 8
[1] 4 9
[1] 5 6
[1] 5 7
[1] 5 8
[1] 5 9
[1]  5 10

解决方案

Why is the 'j' counter exceeding '5' in the inner for loop?

for(j in i+1:5) is equivalent of for(j in i+(1:5)) which can in turn be developed to for(j in (i+1):(i+5))

The reason can be found here

The following unary and binary operators are defined. They are listed in precedence groups, from highest to lowest.

:: :::    access variables in a namespace
$ @   component / slot extraction
[ [[  indexing
^ exponentiation (right to left)
- +   unary minus and plus
: sequence operator ###
%any% special operators (including %% and %/%)
* /   multiply, divide
+ -   (binary) add, subtract ### 

I added the ### to the operators which interest us here, the sequence is of higher precedence than the binary add so adding i will be done to the whole sequence once it has been computed.

If you wish to keep in the range (i+1):5 you have to take care of a special case, where i is 5 as your sequence will become 6:5.

So finally your code could be:

for (i in 1:5){
    s <- min(i+1,5) # Per Ben Bolker comment
    for (j in s:5) {
      print(c(i,j))
    }
}

Which output:

[1] 1 2
[1] 1 3
[1] 1 4
[1] 1 5
[1] 2 3
[1] 2 4
[1] 2 5
[1] 3 4
[1] 3 5
[1] 4 5
[1] 5 5

这篇关于对于R中的“循环不一致”的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！