The sep Parameter

So what does the sep parameter do? It turns out that the sep parameter is only relevant if you are dealing with two or more input vectors; to demonstrate this, let us first make an example vector:

a <- c(1, 2, 3)

Now let us see what happens when we call paste directly on a with sep set to “,”:

paste(a, sep = ", ")

## [1] "1" "2" "3"

We see that the function simply converted the elements in the vector into strings without using the sep.

Let us make another vector:

b <- c("a", "b")

and call paste with both a and b supplied to it:

paste(a, b, sep = ", ")

## [1] "1, a" "2, b" "3, a"

We see that when supplied with more than one vectors, the paste function basically zips together the vectors with recycle and concatenates them using the separator specified by the sep parameter; this process produces a vector of strings.

paste0 is a shorthand for paste(..., sep = ""):

paste0(a, b)

## [1] "1a" "2b" "3a"

The collapse Parameter

The collapse separator is applied to concatenate the vector of strings produced with the sep parameter:

paste(a, b, sep = ", ", collapse = "; ")

## [1] "1, a; 2, b; 3, a"

One of the most common use cases of the paste function is to concatenate the elements in a vector with a separator. To do this, we only need to specify the collapse parameter since sep is irrelevant when dealing with a single input vector:

paste(a, collapse = "; ")

## [1] "1; 2; 3"

Summary

A call to the paste function with both sep and collapse specified performs the following tasks:

1. It first zips together the input vectors with recycle; one can think of this as applying cbind() or rbind() to the input vectors.
2. The function then joins together each zipped tuple using the separator specified by sep; this step produces a vector of strings, one for each zipped tuple.
3. Lastly, the function concatenates the vector of strings produced in the previous step using the separator specified by collapse; this step produces a single string.