我不知道如何在Google上进行搜索。我有彼此独立的行代码-假设一行由于某种原因而失败,那么脚本的其余部分将不会继续。如何使其继续?
例如:
library(RODBC)
library(sqldf)
myconn<-odbcConnect("production")
#行1:sqlQuery(myConn,“ exec sp_v_table_1”)
#line 2:sqlQuery(myConn,“ exec sp_v_table_2”)
此外,我怎么知道某个代码行-例如:
sqlQuery(myConn,"exec sp_v_table_3")
已成功通过但未失败?
您可以使用tryCatch块,您有参考文献here
这里有一个使用它进行请求处理的示例:
urls <- c(
"http://stat.ethz.ch/R-manual/R-devel/library/base/html/connections.html",
"http://en.wikipedia.org/wiki/Xz",
"xxxxx"
)
readUrl <- function(url) {
out <- tryCatch(
{
# Just to highlight: if you want to use more than one
# R expression in the "try" part then you'll have to
# use curly brackets.
# 'tryCatch()' will return the last evaluated expression
# in case the "try" part was completed successfully
message("This is the 'try' part")
readLines(con=url, warn=FALSE)
# The return value of `readLines()` is the actual value
# that will be returned in case there is no condition
# (e.g. warning or error).
# You don't need to state the return value via `return()` as code
# in the "try" part is not wrapped insided a function (unlike that
# for the condition handlers for warnings and error below)
},
error=function(cond) {
message(paste("URL does not seem to exist:", url))
message("Here's the original error message:")
message(cond)
# Choose a return value in case of error
return(NA)
},
warning=function(cond) {
message(paste("URL caused a warning:", url))
message("Here's the original warning message:")
message(cond)
# Choose a return value in case of warning
return(NULL)
},
finally={
# NOTE:
# Here goes everything that should be executed at the end,
# regardless of success or error.
# If you want more than one expression to be executed, then you
# need to wrap them in curly brackets ({...}); otherwise you could
# just have written 'finally=<expression>'
message(paste("Processed URL:", url))
message("Some other message at the end")
}
)
return(out)
}
来源来自this stackoverflow响应,我显然建议您看一下。
您需要一种捕获错误的方法。为此我很欣赏的一个工具是safely()
包中的purrr
。
将您的函数包装在现有函数调用周围,即使发生错误,该函数也可以安全地返回输出。
从文档(log()示例::
safe_log <- safely(log)
safe_log(10)
#> $result
#> [1] 2.302585
#>
#> $error
#> NULL
#>
safe_log("a")
#> $result
#> NULL
#>
#> $error
#> <simpleError in .Primitive("log")(x, base): non-numeric argument to mathematical function>
#>
这将返回一个列表,其中包含结果和错误元素。
使用try
命令。
通常,这将导致错误并阻止随后运行的代码运行:
x <- "a" + 1
y <- 1
y
但是,如果我们在try
中的赋值运算符之后包装零件,则会显示错误,但之后编写的代码仍然可以运行:
x <- try("a" + 1)
y <- 1
y
请注意,x
具有类"try-error"
class(x)
"try-error"
因此,在您的示例中,您可以执行以下操作以确保以后的行能够运行,同时仍然能够拾取之前的行失败:
x <- try(sqlQuery(myConn,"exec sp_v_table_3"))
y <- 1
y
class(x)
仍将创建对象y
,并且x
的类别将告诉您sqlQuery(myConn,"exec sp_v_table_3")
是否成功运行。
tryCatch
在某种意义上是try
的一种更灵活的版本。 try
仅在发生错误时返回类"try-error"
,并允许以后的代码行运行,但是tryCatch
将允许您指定发生错误时要发生的情况。您也可以指定发生warning
或代码成功运行时想要发生的情况。