STATS 782 - Control Flow and Functions

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一、Control Flow

1. If-Then-Else

> if (x > 0) y = sqrt(x) else y = -sqrt(-x)

或
> y = if (x > 0) sqrt(x) else -sqrt(-x)

2. Loops

① for loop：

> x = seq(1, 5)
> x
[1] 1 2 3 4 5

> s = 0
> for (i in x) {
+     s = s + i
+ }
> s
[1] 15

② while loop：

> threshold = 100
> n = 0
> s = 0
> while (s <= threshold) {
	n = n + 1
	s = s + n
}

> c(n, s)
[1] 14 105

二、Functions

1. Defining Functions

> squre <- function(x) {
+     x * x
+ }

> squre(2)
[1] 4
> squre(1:4)
[1]  1  4  9 16

2. 使用函数计算数学公式

# Using a Loop：
> S1 = function(n, k) { # with an explicit loop
s = 0
for (j in 0:k)
s = s + (-1)^(k-j) * choose(k, j) * j^n
s / factorial(k)
}

> S1(10, 3)
[1] 9330
> S1(20, 7)
[1] 1.1144e+13

# No Loop：
> S2 = function(n, k) { # without an explicit loop
j = 0:k
sum((-1)^(k-j) * choose(k, j) * j^n) / factorial(k)
}

> S2(10, 3)
[1] 9330
> S2(20, 7)
[1] 1.1144e+13

总结

本文章对 STATS 782 的第二章节进行了总结，主要涉及控制流语句以及自定义函数的编写。