R: How to make parse() accept regular expressions with escaped characters? - r

Question

I am trying to use the validator package to check if certain rows in my data table contain a regular expression or not.
I make a vector (fields) with the columns I want to test and then paste together the commands for the validator rules as a string.
To be able to use the rules in the confront() function I use parse() and eval() to turn the character string into an expression
The following example is working as expected:
library(validate)
data <- data.frame("Protocol_Number" = c("123", "A122"), "Numeric_Result" = c("-0.5", "1.44"))
fields <- c("Protocol_Number", "Numeric_Result")
# build validator commands for each field
cmds <- paste("validator(",
paste(
map_chr(
fields, function(x) paste0("grepl('^-?[0-9]', as.character(`", x, "`))")
), collapse = ","),
")")
# convert to rule and do the tests
rule <- eval(parse(text = cmds))
out <- confront(data, rule)
summary(out)
However, I want to use a regex that recognizes any sort of number as opposed to text, like in this working example
grepl('^-?[0-9]\\d*(\\.\\d+)?$', c(1, -1, 0.5, "Not Done"))
When I try to use this regex in the above example, the parse() function will throw an error:
Error: '\d' is an unrecognized escape in character string starting "'^-?[0-9]\d"
This is not working:
# build validator commands for each field
cmds <- paste("validator(",
paste(
map_chr(
fields, function(x) paste0("grepl('^-?[0-9]\\d*(\\.\\d+)?$', as.character(`", x, "`))")
), collapse = ","),
")")
# convert to rule and do the tests
rule <- eval(parse(text = cmds))
out <- confront(data, rule)
summary(out)
How do I make parse() accept the escaped characters? Or is there a better way to do this?

Answer 1

We may escape it with \\
cmds <- paste("validator(",
paste(
map_chr(
fields, function(x)
paste0("grepl('^-?[0-9]\\\\d*(\\\\.\\\\d+)?$', as.character(`", x, "`))")
), collapse = ","),
")")
-testing
> rule <- eval(parse(text = cmds))
>
> out <- confront(data, rule)
> out
Object of class 'validation'
Call:
confront(dat = data, x = rule)
Rules confronted: 2
With fails : 1
With missings: 0
Threw warning: 0
Threw error : 0