Combine startsWith and endsWith with R’s pipe

In my first post, startsWith and endsWith were presented. In combination with R’s pipe operator, we can improve the readability even further.

w <- "Hello World!"

w |> startsWith("Hell")
[1] TRUE
w |> endsWith("!")
[1] TRUE

Proceeding with the example of the initial post, let’s see this in context of control flow.

tell_file_type <- function(filename)
{
    if (filename |> endsWith("txt"))
        print("A text file.")
    
    excel_endings <- c("xlsx", "xls")
    if (any(filename |> endsWith(excel_endings)))
        print("An Excel file.")
    
}
tell_file_type("A.xlsx")
[1] "An Excel file."

%in% and %not in%

The %in% operator is commonly used. To improve the readability of something like

existing_names <- c("Lisa", "Bob")
name <- "Peter"
hasNewName = !(name %in% existing_names)

you can always define your own operators.

`%not in%` <- Negate(`%in%`)

hasNewName = name %not in% existing_names

Obviously, the readability also depends on the choice of proper variable names. My general take on this: don’t shy away from longish variable names, if it improves code readability.

In this context, it is often useful to assign boolean values to variables. For example, instead of

if (abs_error < 1e-8) {
    # ...
}

you should do

hasConverged <- abs_error < 1e-8

if (hasConverged) {
    # ...
}

That is, it is ok to add redundancies in your code if it improves readability.

Sometimes, it is not immediately clear from the naming of base R functions, what they do. Of course, you are free to redefine them with a proper name.

equals_pattern = function(x, pattern, ...) grepl(pattern, x, ...)

x <- "Peter"

x |> equals_pattern("^P")
[1] TRUE

Lastly, let’s combine all of the above.

x |> equals_pattern("^P") && 
x |> startsWith("z")      &&
x %not in% existing_names 
[1] FALSE

That’s it for now. Let me know in the comments how you think about this topic or maybe you have another good example of readable code.