Try Catch

Colin Fay

2020-05-03

attempt

attempt() is a wrapper around base try() that allows you to insert a custom messsage on error.

attempt(log("a"))
# Error: non-numeric argument to mathematical function
attempt(log("a"), msg = "Nop !")
# Error: Nop !

You can make it verbose (i.e. returning the expression):

attempt(log("a"), msg = "Nop !", verbose = TRUE)
# Error in log("a"): Nop !

Of course the result is returned if there is one:

attempt(log(1), msg = "Nop !", verbose = TRUE)
# [1] 0

As with try(), the result can be saved as an error object:

a <- attempt(log("a"), msg = "Nop !", verbose = TRUE)
a
# [1] "Error in log(\"a\"): Nop !\n"
# attr(,"class")
# [1] "try-error"
# attr(,"condition")
# <simpleError in log("a"): Nop !>

You can check if the result is an error with is_try_error()

a <- attempt(log("a"), msg = "Nop !", verbose = FALSE)
is_try_error(a)

silent_attempt

silent_attempt() is a wrapper around silently() (see further down for more info) and attempt(). It attempts to run the expr, stays silent if the expression succeeds, and returns error or warnings if any.

silent_attempt(log("a"))
# Error: non-numeric argument to mathematical function
silent_attempt(log(1))

try catch

You can write a try catch with these params:

In .e and .f, the .x refers to the error / warning object.

With mappers

try_catch(expr = log("a"), 
          .e = ~ paste0("There is an error: ", .x), 
          .w = ~ paste0("This is a warning: ", .x))
#[1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"

try_catch(log("a"), 
          .e = ~ stop(.x), 
          .w = ~ warning(.x))
# Error in log("a") : non-numeric argument to mathematical function

try_catch(matrix(1:3, nrow= 2), 
          .e = ~ print(.x), 
          .w = ~ print(.x))
#<simpleWarning in matrix(1:3, nrow = 2): data length [3] is not a sub-multiple or multiple of the number of rows [2]>

try_catch(expr = 2 + 2 , 
          .f = ~ print("Using R for addition... ok I'm out!"))
# [1] "Using R for addition... ok I'm out!"
# [1] 4

As usual, the handlers are set only if you call them:

try_catch(matrix(1:3, nrow = 2), .e = ~ print("error"))
#      [,1] [,2]
# [1,]    1    3
# [2,]    2    1
# Warning message:
# In matrix(1:3, nrow = 2) :
# data length [3] is not a sub-multiple or multiple of the number of rows [2]
try_catch(matrix(1:3, nrow = 2), .w = ~ print("warning"))
# [1] "warning"

Traditionnal way

{attempt} is flexible in how you can specify your arguments.

You can, as you do with {base} tryCatch(), use a plain old function:

try_catch(log("a"), 
          .e = function(e){
            print(paste0("There is an error: ", e))
            print("Ok, let's save this")
            time <- Sys.time()
            a <- paste("+ At",time, ", \nError:",e)
            # write(a, "log.txt", append = TRUE) # commented to prevent log.txt creation 
            print(paste("log saved on log.txt at", time))
            print("let's move on now")
          })

# [1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"
# [1] "Ok, let's save this"
# [1] "log saved on log.txt at 2018-01-30 16:59:13"
# [1] "let's move on now"

You can even mix both:

try_catch(log("a"), 
          .e = function(e){
            paste0("There is an error: ", e)
          },
          .f = ~ print("I'm not sure you can do that pal !"))
# [1] "I'm not sure you can do that pal !"
# [1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"

try_catch(log("a"), 
          .e = ~ paste0("There is an error: ", .x),
          .f = function() print("I'm not sure you can do that pal !"))
# [1] "I'm not sure you can do that pal !"
# [1] "There is an error: Error in log(\"a\"): non-numeric argument to mathematical function\n"

try_catch_df()

try_catch_df() returns a tibble with the call, the error message if any, the warning message if any, and the value of the evaluated expression or “error”. The values will always be contained in a list-column.

res_log <- try_catch_df(log("a"))
res_log
res_log$value

res_matrix <- try_catch_df(matrix(1:3, nrow = 2))
res_matrix
res_matrix$value

res_success <- try_catch_df(log(1))
res_success
res_success$value

map_try_catch()

map_try_catch() and map_try_catch_df() allow you to map on a list of arguments l, to be evaluated by the function in fun.

map_try_catch(l = list(1, 3, "a"), fun = log, .e = ~ .x)

map_try_catch_df(list(1,3,"a"), log)