try-catch method

syntax

# result = tryCatch({
#   expr
# }, warning = function(warning-condition) {
#   warning-handler-code
# }, error = function(error-condition) {
#   error-handler-code
# }, finally={
#   cleanup-code
# })

example1

inputs = list(1, 2, 4, -5, 'oops', 0, 10)

log(1)

## [1] 0

log(2)

## [1] 0.6931472

log(4)

## [1] 1.386294

log(-5)

## Warning in log(-5): NaNs produced

## [1] NaN

#log("oops")
log(0)

## [1] -Inf

log(10)

## [1] 2.302585

log(-(-5))

## [1] 1.609438

Normal for loop

# for(input in inputs) {
#      print(paste("log of", input, "=", log(input)))
# }

#log(-5) #NAN
#log("oops") #error
#its stop then the error occurs

try block

for(input in inputs) {
    try(print(paste("log of", input, "=", log(input))))
   }

## [1] "log of 1 = 0"
## [1] "log of 2 = 0.693147180559945"
## [1] "log of 4 = 1.38629436111989"

## Warning in log(input): NaNs produced

## [1] "log of -5 = NaN"
## [1] "log of 0 = -Inf"
## [1] "log of 10 = 2.30258509299405"

#This skips over the error-causing non-numeric input with an error message 
#(you can suppress the error message with the silent=T argument to try), 
#and continues on with the rest of the input.

for(input in inputs) {
  try(print(paste("log of", input, "=", log(input))),silent = T)
}#removes error

## [1] "log of 1 = 0"
## [1] "log of 2 = 0.693147180559945"
## [1] "log of 4 = 1.38629436111989"

## Warning in log(input): NaNs produced

## [1] "log of -5 = NaN"
## [1] "log of 0 = -Inf"
## [1] "log of 10 = 2.30258509299405"

trycatch block

1

for(input in inputs) {
  tryCatch(print(paste("log of", input, "=", log(input))),
           warning = function(w) {print(paste("negative argument", input))},
            error = function(e) {print(paste("non-numeric argument", input))}
           )}

## [1] "log of 1 = 0"
## [1] "log of 2 = 0.693147180559945"
## [1] "log of 4 = 1.38629436111989"
## [1] "negative argument -5"
## [1] "non-numeric argument oops"
## [1] "log of 0 = -Inf"
## [1] "log of 10 = 2.30258509299405"

2

robustLog = function(x) {
    tryCatch(log(x),
          warning = function(w) {print(paste("negative argument", x)); 
             log(-x)},
          error = function(e) {print(paste("non-numeric argument", x)); 
                 NaN}) 
  }

 for(input in inputs) {
     print(paste("robust log of", input, "=", robustLog(input)))
}

## [1] "robust log of 1 = 0"
## [1] "robust log of 2 = 0.693147180559945"
## [1] "robust log of 4 = 1.38629436111989"
## [1] "negative argument -5"
## [1] "robust log of -5 = 1.6094379124341"
## [1] "non-numeric argument oops"
## [1] "robust log of oops = NaN"
## [1] "robust log of 0 = -Inf"
## [1] "robust log of 10 = 2.30258509299405"

example

a<-list(1,2,3,4,-4,5,0,10,"sujith")
#sqrt(a)
a_sqrt<-list()
we <- function(x) {
  tryCatch(sqrt(x),
           warning = function(w){ print("warning");
               sqrt(-x)},
            error  = function(e){print("error");
                NaN })
           }
    

for(i in a){
  print(paste("squareroot of ",i,"=",we(i)))
  a_sqrt<-append(a_sqrt,we(i))
}

## [1] "squareroot of  1 = 1"
## [1] "squareroot of  2 = 1.4142135623731"
## [1] "squareroot of  3 = 1.73205080756888"
## [1] "squareroot of  4 = 2"
## [1] "warning"
## [1] "squareroot of  -4 = 2"
## [1] "warning"
## [1] "squareroot of  5 = 2.23606797749979"
## [1] "squareroot of  0 = 0"
## [1] "squareroot of  10 = 3.16227766016838"
## [1] "error"
## [1] "squareroot of  sujith = NaN"
## [1] "error"

a_sqrt

## [[1]]
## [1] 1
## 
## [[2]]
## [1] 1.414214
## 
## [[3]]
## [1] 1.732051
## 
## [[4]]
## [1] 2
## 
## [[5]]
## [1] 2
## 
## [[6]]
## [1] 2.236068
## 
## [[7]]
## [1] 0
## 
## [[8]]
## [1] 3.162278
## 
## [[9]]
## [1] NaN