我正在尝试在for循环中处理两个可能的错误，该循环调用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具体措施。
如果我仅尝试处理一种可能的错误，则它可以起作用：
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。我在做什么错了？
非常感谢您的帮助。
编辑
在马丁明确解释之后，我试图将所有内容放入函数中。它不起作用。
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)
然后函数将继续并返回一个空对象。配额结束且错误为：
You have exceeded your daily request quota for this API.
它递归地返回一个错误，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。
答案 0 :(得分：3)
有两种捕获错误类型的方法，这取决于错误的产生方式。这是一个会产生错误的函数
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”，则该函数会生成标准错误条件，但带有不同的条件消息（“ oops a：...”和“ oops b：...”） 。如果type为“ 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。类型“ a”或“ b”的错误具有相同的类，因此由同一处理程序捕获；区分它们的唯一选择是“抓取”错误消息以查看条件（错误）消息，以确定一个人正在处理的错误的类型（希望程序包不那么复杂以至于包括错误消息翻译，例如base R可以，因为通常不可能以健壮的方式抓取翻译后的错误...）
> 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，处理程序可以捕获类型“ c”，因为它具有自己的类。所以...
> g("c")
found custom_error: oop 2: custom error class
一个人实际上可以沿着错误处理程序或向上调用堆栈传递错误
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)
})
}
使用
> h("c")
found custom_error: oop 2: custom error class
found an error: oop 2: custom error class
Error: oop 2: custom error class
很少有软件包实际使用犯自定义错误的功能，因此您可能会想尝试抓取您看到的错误。对于您的情况，看来您必须抓取，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
}
})