[英]How to add Results into a Vector within a Loop in R
I was prompted a question and am ever so close to solving what I need.我被提示了一个问题,并且非常接近解决我需要的问题。 The question is as follows-问题如下——
"Write a while loop that computes and stores as a new object, the factorial of any non-negative integer mynum by decrementing mynum by 1 at each repetition of the braced code." “编写一个 while 循环,计算并存储为新的 object,任何非负 integer mynum 的阶乘,方法是在每次重复括号代码时将 mynum 减 1。”
Another factor was that if 0 or 1 was entered, the output would be 1.另一个因素是,如果输入 0 或 1,则 output 将为 1。
The code that I wrote as follows-我写的代码如下-
factorialcalc <- function(i){
factorial <- 1
if(i==0 | i==1){
factorial <- 1
} else{
while(i >= 1){
factorial <- factorial * i
i <- i-1
}
}
return (factorial)
}
with inputs-与输入-
mynum <- 5
factorialcalc(mynum)
and output-和输出-
[1] 120
You may be wondering, "your code works perfect, so what's the issue?"您可能想知道,“您的代码运行良好,那么问题出在哪里?” My issue lies in the part of the question that says "computes AND stores."我的问题在于“计算和存储”的问题部分。
How can I modify my code to put the answers of factorialcalc into a vector?如何修改我的代码以将 factorialcalc 的答案放入向量中?
Example- I input示例-我输入
mynum <- 5
factorialcalc(mynum)
and和
mynum <- 3
factorialcalc(mynum)
and和
mynum <- 4
factorialcalc(mynum)
When I call this new vector, I would like to see a vector with all three of their outputs (so almost like I made a vector c(120,6,24))当我调用这个新向量时,我希望看到一个包含所有三个输出的向量(就像我制作了一个向量 c(120,6,24))
I'm thinking there's a way to add this vector somewhere in my function or while loop, but I'm not sure where.我在想有一种方法可以在我的 function 或 while 循环中的某处添加这个向量,但我不确定在哪里。 Also, please note that the answer must contain a loop like in my code.另外,请注意答案必须包含我的代码中的循环。
The answer I would be looking for would have an empty vector say answers <- c()
, and every time I were to run the function factorialcalc
, during the function, I would add the return results from factorial
into this new answers
vector.我要寻找的答案将有一个空向量说answers <- c()
,并且每次我要运行 function factorialcalc
,在 function 期间,我会将factorial
的返回结果添加到这个新的answers
向量中。
I've tried putting in something like this-我试过放这样的东西-
factorialcalc <- function(i){
factorial <- 1
answers <- c()
answers[i] <- answers[factorial]
if(i==0 | i==1){
factorial <- 1
} else{
while(i >= 1){
factorial <- factorial * i
i <- i-1
}
}
return (factorial)
}
This doesn't seem to work, but I think the idea is there.这似乎不起作用,但我认为这个想法是存在的。
Thanks in advance for any help.提前感谢您的帮助。
Here is a solution that illustrates how to build a vector of results for a factorial function.这是一个解决方案,说明了如何为阶乘 function 构建结果向量。 We use the testthat
package to build unit tests for the function.我们使用testthat
测试为 function 构建单元测试。
Rather than iterating from i
down to 1, we iterate from 2 to i
, using the j-1
value in the output vector to multiply by the current number in the for()
loop.我们不是从i
迭代到 1 ,而是从 2 迭代到i
,使用 output 向量中的j-1
值乘以for()
循环中的当前数字。
We also include error checking at the top of the function.我们还在 function 的顶部包括错误检查。 Since R does not have a way to directly validate a numeric vector as an integer / whole number, we compare the absolute value of the input minus its rounded value to machine precision and stop if the comparison fails.由于 R 无法直接将数字向量验证为 integer / 整数,因此我们将输入的绝对值减去其舍入值与机器精度进行比较,如果比较失败则停止。
factorial <- function(i){
# return a vector of factorial values from 1 to i, where
# i represents the i-th value in the factorial series
# first, validate the input
if(!is.numeric(i)) stop("i must be a whole number")
if(!(abs(i - round(i)) < .Machine$double.eps^0.5)) stop("i must be a whole number")
if (i < 0) stop("i must be a whole number")
# now, process based on value of i
if (i %in% c(0,1)) return(1)
resultVector <- 1
# if we get here, i is greater than 1
for(j in 2:i) resultVector <- c(resultVector,resultVector[j-1]*j)
resultVector
}
We test the function with a variety of tests, ranging from invalid input handling to confirming the output of the function with known values.我们通过各种测试来测试 function,范围从无效输入处理到确认 function 的 output 具有已知值。 We also compare the length of the output vector to the input value of i
.我们还将 output 向量的长度与i
的输入值进行比较。
library(testthat)
test_that("Factorial function works",{
expect_error(factorial(-3),"i must be a whole number",ignore.case=TRUE)
expect_equal(1,factorial(0))
expect_equal(1,factorial(1))
expect_equal(c(1,2),factorial(2))
expect_equal(c(1,2,6),factorial(3))
expect_equal(c(1,2,6,24),factorial(4))
expect_equal(c(1,2,6,24,120),factorial(5))
expect_equal(5,length(factorial(5))) # test that length matches input i
expect_error(factorial(3.1),"i must be a whole number",ignore.case=TRUE)
expect_error(factorial("zzz"),"i must be a whole number",ignore.case=TRUE)
})
...and the test results: ...和测试结果:
==> Testing R file using 'testthat'
✓ | OK F W S | Context
✓ | 10 | factorial
══ Results ═════════════════════════════════════════════════════════════════════
Duration: 0.2 s
OK: 10
Failed: 0
Warnings: 0
Skipped: 0
Test complete
Finally, we run the function multiple times to illustrate its output:最后,我们多次运行function来说明它的output:
> lapply(1:8,factorial)
[[1]]
[1] 1
[[2]]
[1] 1 2
[[3]]
[1] 1 2 6
[[4]]
[1] 1 2 6 24
[[5]]
[1] 1 2 6 24 120
[[6]]
[1] 1 2 6 24 120 720
[[7]]
[1] 1 2 6 24 120 720 5040
[[8]]
[1] 1 2 6 24 120 720 5040 40320
Consider Reduce
first as replacement of your method:首先考虑Reduce
作为您的方法的替代:
Reduce(`*`, 1:5)
# [1] 120
To extend incrementally, pass a sequence with Reduce
inside an apply function (only mapply
needs adjustment due to multiple elements):要增量扩展,请在 apply function 中传递一个带有Reduce
的序列(由于多个元素,只有mapply
需要调整):
factorialcalc <- function(i) Reduce(`*`, 1:i)
sapply(1:5, factorialcalc)
# [1] 1 2 6 24 120
vapply(1:5, factorialcalc, integer(1))
# [1] 1 2 6 24 120
tapply(1:5, 1:5, factorialcalc)
# 1 2 3 4 5
# 1 2 6 24 120
factorialcalc <- function(i,j) Reduce(`*`, i:j)
mapply(factorialcalc, 1, 1:5)
# [1] 1 2 6 24 120
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