r - R中的tryCatch block ，返回变量

Question

因此，我试图了解R中tryCatch的范围和功能。

下一行:

arima(rep(1,3), order = c(1,0,0))

生成警告和错误，但是在tryCatch块中，仅警告函数返回值。如何获得警告和错误的返回值？

tryTest = tryCatch(
  {
    arima(rep(1,3), order = c(1,0,0))
  }, 
  warning = function(w) {

    print('this is warning')
    print(w)
    return('return string from warning')
  },
  error = function(e) {
    print('this is error')
    print(e)
    return('return string from error')
  },
  finally = {}
)

print(tryTest)

仅产生:

 "return string from warning"

Answer 1

R中的tryCatch允许您在出错时为变量分配一个值。这是两个最小的示例:

my_logo <- tryCatch(
{
  my_logo <- RCurl::getURLContent("https://invalid.website")
},
error = function(cond){
  my_logo <- "there is no image"
},
finally = {
  #pass
})

> my_logo
[1] "there is no image"

my_var <- tryCatch(
{
  my_var <- "a"/1
},
error = function(cond){
  my_var <- "foo"
},
finally = {
  #pass
})

> my_var
[1] "foo"

同样，您可以知道一个警告值。您不应编写tryCatch语句，以使其可能同时遇到错误和警告。我什至不确定这是否可行。

编辑:为了完整性，我添加了一个警告示例:

my_var <- tryCatch(
{
  warning()
  my_var <- "a"/1
},
warning = function(cond){
  print("There was a warning")
  return("bar")
},
error = function(cond){
  my_var <- "foo"
  print("This message will not be printed.")
},
finally = {
  #pass
})
[1] "There was a warning"
> my_var
[1] "bar"