Shiny validate for read.csv - r

Question

I am trying to use shiny validate function to capture reading errors and show customized error message when reading uploaded csv files instead of letting shiny forward the default read.csv error message.
Here is the simple code
validate(need(try(sd <- read.csv(file = sdFile[1], stringsAsFactors = FALSE)), "Error reading the file"))
when there is no format issue in the csv file, the code works normally. But when there is an issue with the csv file, the code still returns the default error message (in red font), eg., Error: undefined columns selected, but not the customized message. Any issue here? Thanks!

Answer 1

I think it is actually printing it out, if I do this:
library(shiny)
validate(need(try(sd <- read.csv(file = "mtcars1.csv",
stringsAsFactors = FALSE)),
Error reading the file !!!"))
yielding:
Error in file(file, "rt") : cannot open the connection
In addition: Warning message:
In file(file, "rt") :
cannot open file 'mtcars1.csv': No such file or directory
Error: Error reading the file !!!
I get this - note your message is the in the last line.
You can suppress the warnings with supressWarnings like this:
library(shiny)
suppressWarnings(
+ validate(need(try(sd <- read.csv(file = "mtcars1.csv",
stringsAsFactors = FALSE)),
"Error reading the file !!!!")))
yielding:
Error in file(file, "rt") : cannot open the connection
Error: Error reading the file !!!!
Or you can supress everything but your message with this (uses tryCatch instead of try):
library(shiny)
suppressWarnings(
validate(need(tryCatch(sd <- read.csv(file = "mtcars1.csv",
stringsAsFactors = FALSE), error=function (e){}),
"Error reading the file !!!!")))
yielding
Error: Error reading the file !!!