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Force argument to have quotes

4 messages · Doran, Harold, Boris Steipe, Bert Gunter +1 more

Doran, Harold
# 
I am writing a program where non-technical R users will read in a config file and the config file will then parse the arguments found within the config and pass them to respective functions. I'm having trouble (efficiently) writing a piece of code to retain quotation marks around the argument which requires it as input, as found in the example function below, myFuncton1.

Below is a minimal, reproducible example of the issue with comments.

### This is a sample structure of the configuration file

scoreConfig <- structure(list(Function = c("myFunction1", "myFunction1", "myFunction1", 
"myFunction2", "myFunction2"), Argument = c("arg1", "arg2", "arg3", 
"arg1", "arg2"), Value = c("5", "10", "Hello", "5", "10"), Class = c("numeric", 
"numeric", "character", "numeric", "numeric")), .Names = c("Function", 
"Argument", "Value", "Class"), class = "data.frame", row.names = c(NA, 
-5L))

### Two sample functions, once of which requires a string
myFunction1 <- function(arg1, arg2, arg3 = c('Hello', 'Goodbye')){
	arg3 <- match.arg(arg3)
	result <- arg1 + arg2
	cat(arg3, result, '\n')
	}
	
	
myFunction2 <- function(arg1, arg2){
	result <- arg1 * arg2
	result
	}


### Working Example. 
### myFunction2 works no problem
myFunction2Vals <- subset(scoreConfig, Function == 'myFunction2')
myOptions <- with(myFunction2Vals, paste(Argument, Value, sep = '=', collapse = ','))
eval(parse(text = paste( "myFunction2(", myOptions, ")" )))


### myFunction1 fails 
myFunction1Vals <- subset(scoreConfig, Function == 'myFunction1')
myOptions <- with(myFunction1Vals, paste(Argument, Value, sep = '=', collapse = ','))
eval(parse(text = paste( "myFunction1(", myOptions, ")" )))

### What I want is simply
myFunction1(arg1 = 1, arg2 = 2, arg3 = 'Hello')

I'm curious if someone has a perspective on the most efficient way to automate this by using information provided in the 'Value" column, so perhaps conditional on that value it could wrap the name in quotes.

I admit to running into a limit and am tapping out so to speak on the right way to do this.

Thanks for any advice
Harold
Boris Steipe
# 
If I understand you correctly what you are really asking is how to embed quotes in a string so that it can be parse()'d as an expression. The answer would be: escape the quotes.


R > myOptions <- "Hello"
R > eval(parse(text = paste( "print(", myOptions, ")" )))
 Error in print(Hello) : object 'Hello' not found 

R > eval(parse(text = paste( "print( \"", myOptions, "\")", sep="" )))
[1] "Hello"

(Myself, I would use sprintf(),

R > myFunction <- "print"
R > eval(parse(text = sprintf("%s(\"%s\")", myFunction, myOptions)))
[1] "Hello"

)


Ask again if this is only part of the problem.

B.
Bert Gunter
# 
Harold:

As a general rule, if you are using eval(parse(...)) you are doing it
poorly in R; cf

library("fortunes")
fortune(106)

Why is something like this not suitable:

fun1 <- function(a1,a2,a3 = c("hi","by"))
{
   cat(a3,a1+a2,"\n")
}
hi by 3
whoopee 3

... or, if you want to include the function as an argument of a list:
For which you can do stuff like:
hi by 7
whoopee 7

etc. etc.
See ?do.call

Cheers,
Bert



Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Tue, Jun 6, 2017 at 8:01 AM, Doran, Harold <HDoran at air.org> wrote:
Nordlund, Dan (DSHS/RDA)
# 
Bert has suggested there are better ways to do what you want.  But if you want to continue down the path you have started and you want to decide whether to quote based on the variable Class, something like this might work for you  

myOptions <- with(myFunction1Vals, paste(Argument, ifelse(Class=='character',shQuote(Value), Value), sep = '=', collapse = ","))


Hope this helps,

Dan

Daniel Nordlund, PhD
Research and Data Analysis Division
Services & Enterprise Support Administration
Washington State Department of Social and Health Services