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程序问答发布时间：2022-06-02 发布网站：大佬教程 code.js-code.com

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如何解决如何使用 Trycatch 跳过 R 中数据下载中的错误？

开发过程中遇到如何使用 Trycatch 跳过 R 中数据下载中的错误的问题如何解决？下面主要结合日常开发的经验，给出你关于如何使用 Trycatch 跳过 R 中数据下载中的错误的解决方法建议，希望对你解决如何使用 Trycatch 跳过 R 中数据下载中的错误有所启发或帮助；

我正在尝试使用 R 的 dataRetrIEval 包从 USGS 网站下载数据。

为此，我在 R 中生成了一个名为 getstreamflow 的函数，例如，当我运行时它可以正常工作。

sitenumber <- c("094985005","09498501","09489500","09489499","09498502")
Streamflow = getstreamflow(sitenumber)

函数的输出是一个数据框列表

如何使用 Trycatch 跳过 R 中数据下载中的错误

我可以在下载数据没有问题的情况下运行该功能，但对于某些站点，我收到以下错误：

request Failed [404]. retrying in 1.1 seconds...
request Failed [404]. retrying in 3.3 seconds...
For: https://waterserviceS.Usgs.gov/nwis/site/?siteOutput=Expanded&format=rdb&site=0946666666

为避免函数在遇到错误时停止，我尝试使用 tryCatch，如下代码所示：

Streamflow = tryCatch(
  expr = {
    getstreamflow(sitenumber)
  },error = function(E) {
  message(paste(sitenumber," there was an error"))
})

我希望函数在遇到错误时跳过该站并转到下一个。目前，我得到的输出是下面显示的输出，这显然是错误的，因为它说所有站都存在错误：

094985005 there was an error09498501 there was an error09489500 there was an error09489499 there was an error09498502 there was an error09511300 there was an error09498400 there was an error09498500 there was an error09489700 there was an error09500500 there was an error09489082 there was an error09510200 there was an error09489100 there was an error09490500 there was an error09510180 there was an error09494000 there was an error09490000 there was an error09489086 there was an error09489089 there was an error09489200 there was an error09489078 there was an error09510170 there was an error09493500 there was an error09493000 there was an error09498503 there was an error09497500 there was an error09510000 there was an error09509502 there was an error09509500 there was an error09492400 there was an error09492500 there was an error09497980 there was an error09497850 there was an error09492000 there was an error09497800 there was an error09510150 there was an error09499500 there was an error... <truncated>

我在使用 tryCatch 时做错了什么？

解决方法

回答

您在 tryCatch 之外编写了 getstreamflow。因此，如果一个站点失败，那么 getstreamflow 将返回一个错误而不是其他任何内容。您应该一次提供 1 个站点，或者将 tryCatch 放在 getstreamflow 中。

示例

x <- 1:5
fun <- function(X) {
  for (i in X) if (i == 5) stop("ERROR")
  return(x^2)
}

tryCatch(fun(X),error = function(E) paste0("wrong",X))

[1] "wrong1" "wrong2" "wrong3" "wrong4" "wrong5"

多个参数

您表示您有 sitenumber 和 datatype 可以迭代。

使用 @H_908_3@map，我们可以定义一个接受两个输入的函数：

@H_908_3@map(function(x,y) tryCatch(fun(x,y),error = function(E) message(paste(x," there was an error"))),x = sitenumber,y = datatypE)

使用 for 循环，我们可以遍历它们：

Streamflow <- vector(mode = "list",length = length(sitenumber))
for (i in seq_along(sitenumber)) {
  Streamflow[[i]] <- tryCatch(getstreamflow(sitenumber[i],datatypE)," there was an error")))
}

或者，按照建议，只需修改 getstreamflow。