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I was wondering how one might go about writing a string concatenation operator in R, something like || in SAS, + in Java/C# or & in Visual Basic.
The easiest way would be to create a special operator using %, like
`%+%` <- function(a, b) paste(a, b, sep="") but this leads to lots of ugly %'s in the code.
I noticed that + is defined in the Ops group, and you can write S4 methods for that group, so perhaps something like that would be the way to go. However, I have no experience with S4 language features at all. How would I modify the above function to use S4?
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Concatenate two strings # use cbind method to bind the strings into a vector. vec < - cbind(string1, string2) # combined vector. # use paste() function to perform string concatenation. # elements are joined together.
First, we used the paste() function from base R. Using this function, we combined two and three columns, changed the separator from whitespaces to hyphen (“-”). Second, we used the str_() function to merge columns. Third, we used the unite() function.
The same + operator you use for adding two numbers can be used to concatenate two strings. You can also use += , where a += b is a shorthand for a = a + b .
The & operator is recommended for string concatenation because it is defined exclusively for strings and reduces your chances of generating an unintended conversion.
As others have mentioned, you cannot override the sealed S4 method "+". However, you do not need to define a new class in order to define an addition function for strings; this is not ideal since it forces you to convert the class of strings and thus leading to more ugly code. Instead, one can simply overwrite the "+" function:
"+" = function(x,y) { if(is.character(x) || is.character(y)) { return(paste(x , y, sep="")) } else { .Primitive("+")(x,y) } } Then the following should all work as expected:
1 + 4 1:10 + 4 "Help" + "Me" This solution feels a bit like a hack, since you are no longer using formal methods but its the only way to get the exact behavior you wanted.
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