我正在尝试处理for循环中的两个可能的错误，该循环要求stplanr::dist_google与API进行交互。我知道这些错误，因此我想在发生错误时采取特定的措施。
如果我尝试仅处理可能的错误之一，则它可以工作：
data(cents, package = "stplanr")
data(flow, package = "stplanr")
od <- stplanr::od2odf(flow=flow, zones=cents)
uma_linha <- data.frame(from_addresses=NA, to_addresses=NA, distances=NA,
duration=NA, currency=NA, fare=NA)
output <- data.frame()
for (linha in 1:nrow(od)) {
o <- od[linha, 3:4]
d <- od[linha, 5:6]
output <- tryCatch(
{
rbind(output, stplanr::dist_google(from = o, to = d,
mode = 'walking'))
},
error = function(na) {
message("Erro: No results for this request (e.g. due to lack of support for this mode between the from and to locations)")
message(na)
output <- rbind(output, uma_linha)
}
)
}
我需要获得2500多个观察结果。然后，自动使用两个API。我试图将其他信息和一些小技巧作为一种动作。当我调用循环时，我反复收到两条错误消息。
n <- 1
apis <- c("api01", "api02", "api03")
for (linha in 1:nrow(od)) {
o <- od[linha, 3:4]
d <- od[linha, 5:6]
output <- tryCatch(
{
rbind(output, stplanr::dist_google(from = o, to = d,
mode = 'walking',
google_api = apis[n]))
},
error = function(na) {
message("Erro: No results for this request (e.g. due to lack of support for this mode between the from and to locations)")
message(na)
output <- rbind(output, uma_linha)
},
error = function(quota) {
message("Erro: You have exceeded your daily request quota for this API.")
message(quota)
n <- n + 1
return(n)
}
)
}
我对tryCatch感到困惑。我究竟做错了什么？
非常感谢您的帮助。
编辑
在Martin明确解释之后，我尝试将所有内容放入函数中。没用
如果错误是：
No results for this request (e.g. due to lack of support for this mode between the from and to locations)
然后该函数将继续执行并返回一个空对象。配额结束时，错误为：
You have exceeded your daily request quota for this API.
它递归地返回错误，而不是执行n <- n + 1并继续循环：
asha_dists <- function(fluxo, zonas, api) {
zonas <- as(st_transform(zonas, 4326), "Spatial")
od <- stplanr::od2odf(flow = fluxo, zones = zonas)
uma_linha <- data.frame(from_addresses=NA, to_addresses=NA, distances=NA,
duration=NA, currency=NA, fare=NA)
n <- 1
output <- data.frame()
for (linha in 1:nrow(od)) {
o <- od[linha, 3:4]
d <- od[linha, 5:6]
output <- tryCatch(
{
rbind(output, stplanr::dist_google(from = o, to = d,
mode = 'walking', google_api = api[n]))
},
custom_error = function(e) {
err <- conditionMessage(e)
message("found custom_error: ", err)
output <- rbind(output, uma_linha)
},
error = function(e) {
err <- conditionMessage(e)
message("found an error: ", err)
n <- n + 1
}
)
}
return(output)
}
Sent this request: https://maps.googleapis.com/maps/api/distancematrix/json?units=metric&origins=-23.5678377804732,-46.5708261676873&destinations=-23.5706647015703,-46.5755950203842&mode=walking&key=AIzaSyBRPrAjSE_pRMWSq_XlO4BFwGD63j_gB4U
found an error: You have exceeded your daily request quota for this API.
Sent this request: https://maps.googleapis.com/maps/api/distancematrix/json?units=metric&origins=-23.5665596480444,-46.5682308348154&destinations=-23.5706647015703,-46.5755950203842&mode=walking&key=AIzaSyBRPrAjSE_pRMWSq_XlO4BFwGD63j_gB4U
found an error: You have exceeded your daily request quota for this API.
我只是被困住了。
有两种方法可以捕获错误类型，这取决于错误是如何生成的。这是一个产生错误的函数
f <- function(type) {
switch(
type,
a = stop("oops a: type 1 error"),
b = stop("oops b: type 2 error"),
c = {
err <- simpleError("oop 2: custom error class")
class(err) <- c("custom_error", class(err))
stop(err)
}
)
}
如果type是“a”或“b”，则该函数生成标准错误条件，但具有不同的条件消息（“oops a：...”和“oops b：...”）。如果type是“c”，则该错误具有特定的类“custom_error”，该类扩展了标准错误的 (S3) 类。
> f("a")
Error in f("a") : oops a: type 1 error
> f("b")
Error in f("b") : oops b: type 2 error
> f("c")
Error: oop 2: custom error class
这是一个捕获错误的函数。
g <- function(type) {
tryCatch({
f(type)
}, custom_error = function(e) {
err <- conditionMessage(e)
message("found custom_error: ", err)
}, error = function(e) {
err <- conditionMessage(e)
if (startsWith(err, "oops a")) {
message("found type 'a' error: ", err)
} else if (startsWith(err, "oops b")) {
message("found type 'b' error: ", err)
} else {
message("generic error: ", err)
}
})
}
tryCatch 的处理程序参数按照它们在参数列表中出现的顺序进行测试，如果它们与错误的类匹配，则对它们进行评估。“a”或“b”类型的错误具有相同的类，因此由相同的处理程序捕获；区分它们的唯一选择是“抓取”错误消息，查看条件（错误）消息以确定正在处理的错误类型（希望该包不要复杂到包含错误消息翻译，例如基础 R 确实如此，因为通常不可能以稳健的方式消除翻译错误......）
> g("a")
found type 'a' error: oops a: type 1 error
> g("b")
found type 'b' error: oops b: type 2 error
另一方面，类型“c”可以被处理程序捕获，因为它有自己的类。所以...
> g("c")
found custom_error: oop 2: custom error class
实际上可以沿着错误处理程序或调用堆栈向上传递错误
h <- function(type) {
tryCatch({
f(type)
}, custom_error = function(e) {
err <- conditionMessage(e)
message("found custom_error: ", err)
stop(e)
}, error = function(e) {
err <- conditionMessage(e)
message("found an error: ", err)
stop(e)
})
}
和
> h("c")
found custom_error: oop 2: custom error class
found an error: oop 2: custom error class
Error: oop 2: custom error class
很少有软件包实际上使用了产生自定义错误的功能，因此您可能会一直试图清除所看到的错误。对于你的情况，看来你必须刮，所以
output <- tryCatch({
rbind(
output,
stplanr::dist_google(
from = o, to = d, mode = 'walking', google_api = api[n]
)
)
}, error = function(e) {
err <- conditionMessage(e)
if (startsWith("No results for this request", err) {
warning(err) # warn instead of error
n <<- n + 1 # '<<-' to update n _outside_ this function
rbind(output, uma_linha) # empty output as result
} else if (startsWith("You have exceeded your daily", err) {
stop(e) # signal the original error
} else {
stop(e) # no error that we know how to handle, signal
}
})