立刻停止

R 防御式编程

Dr. Colin Gillespie

Jumping Rivers

我看到了信号

有时事情就是坏了

我们需要抛出错误

例如：

1 + "stuff"

Error in 1 + "stuff": non-numeric argument to binary operator

现在就停止，谢谢合作

要抛出错误，使用 stop() 函数

stop("A Euro 1996 error has occurred")

# Error: A Euro 1996 error has occurred

conf_int <- function(mean, std_dev) {
   if(std_dev <= 0) 
       stop("Standard deviation must be positive")

   c(mean - 1.96 * std_dev, mean - 1.96 * std_dev)
}

尽快捕获

你无法抑制（或忽略）错误
- 错误的定义是 R 无法继续
- 我们改为捕获错误

try() 函数

try() 有点像 suppress()

res <- try("Scotland" + "World cup", silent = TRUE)

它尝试执行；若失败，则继续向下运行

try() 的惯用法

res <- try("Scotland" + "World cup", silent = TRUE)
res

[1] 'Error in "Scotland" + "World cup": non-numeric argument to binary operator'
attr(,"class")
[1] "try-error"
attr(,"condition")
<simpleError in "Scotland" + "World cup": 
                            non-numeric argument to binary operator>

try() 的惯用法

result <- try("Scotland" + "World cup", silent = TRUE)
class(result)

[1] "try-error"

if(class(result) == "try-error")
  ## Do something useful

Vamos praticar!

R 防御式编程