Debugging

Optimizing R Code with Rcpp

Romain François

Consulting Datactive, ThinkR

Print to the console

A function that uses Rprintf() to print a message on the console

cppFunction( '
int fun(){  

    // Some values
    int x = 42 ;

    // Printing a message to the R console
    Rprintf( "some message in the console, x=%d\\n", x ) ;

    // Return some int
    return 76 ;
}
')

Rprintf and placeholders

Integer placeholder with %d

int x = 42 ;

Rprintf( "some message in the console, x=%d\n", x ) ;

// Prints the following in the console: 
some message in the console, x=42

String placeholder with %s

Rprintf( "roses are %s, violets are %s\n", "red", "blue" ) ;

// Prints the following:
roses are red, violets are blue

A function that uses Rprintf() to print a message on the console

cppFunction( 'int fun(){  
    // some values
    int x = 42 ;

    // printing a message to the R console
    Rprintf( "some message in the console, x=%d\\n", x ) ;

    // return some int
    return 76 ;}     ')

Calling the function

fun()

some message in the console, x=42
76

Error messages

A function that only takes numbers between 0 and 20

cppFunction( 'int fun(int x){  
    // A simple error message
    if( x < 0 ) stop( "sorry x should be positive" ) ;    
    // A formatted error message 
    if( x > 20 ) stop( "x is too big (x=%d)", x ) ;    
    // Return some int
    return x ;     }')

fun(-2)

Error in fun(-2) : sorry x should be positive

Error messages

fun(23)

Error in fun(23) : x is too big (x=23)

tryCatch( fun(24), error = function(e){
    message("C++ exception caught: ", conditionMessage(e))
})

C++ exception caught: x is too big (x=24)

Let's practice!

Optimizing R Code with Rcpp