Function Specification for Implicit Renaming

We wish to specify the function to be applied to the current column names to generate the desired names.

In this section, we cover the following function specification scenarios:

  • Named Function where we cover how to apply a built-in function or a custom function to each column name. The column names will be passed one by one as a string and the function and the function is expected to return a single string each time.
  • Anonymous Function where we cover how to apply a lambda function to each column name. Passing an anonymous (lambda) function which works similarly to a function but is often more convenient especially when parameters need to be passed.

The examples we show here rename all columns of a data frame. See Column Selection for Implicit Renaming for how to apply the renaming function to a selected set of columns only.

Named Function

We wish to rename columns by applying a named function to the current column names to generate the desired column names.

Built-In Function

In this example, we wish to convert the upper-case column names to lower-case.

df_2 = df %>% rename_with(str_to_lower)

Here is how this works:

  • We use the function rename_with() from the dplyr package to apply a function to the current column names to generate the desired column names.
  • We pass to rename_with() the name of the function that we wish to apply to each column name, which here is str_to_lower().
  • The column names are passed at once to the passed function as a vector. The function is expected to return a vector of string values of the same size.
  • In this solution, the renaming logic is applied to all columns. See Column Selection for Implicit Renaming for how to apply the renaming function to a selected set of columns only.

Custom Function

In this example, we wish to have column names follow the template 'col_{col}_v2' where {col} is the current column name.

format_name <- function(p_col) {
  str_glue('col_{p_col}_v2')
}

df_2 = df %>% rename_with(format_name)

Here is how this works:

  • This works similarly to the “Built-In Function” scenario described above except that we pass to rename_with our custom function format_name().
  • We use the function str_glue() to insert each current column name in the desired naming template. See String Interpolation.

Anonymous Function

We wish to rename columns by applying a lambda function to the current column names to generate the desired column names.

df_2 = df %>% 
  rename_with(~ str_trim(.) %>% 
                str_to_lower() %>% 
                str_replace_all(' ', '_'))

Here is how this works:

  • This works similarly to the Named Function scenario described above except that we pass to rename_with() an anonymous function (i.e. a one-sided formula).

  • In this example, the anonymous function takes a column name and applies a set of string manipulation operations.

    • removes leading and trailing spaces via str_trim()
    • converts the name to lower-case via str_to_lower()
    • and replaces spaces with underscores via str_replace_all()

    See String Operations.

  • In this solution, the renaming logic is applied to all columns. See Column Selection for Implicit Renaming for how to apply the renaming function to a selected set of columns only.

R
I/O