Example: Splitting Text
Separate text without inventing information
A label can contain several pieces of information. First split the text mechanically; then decide what each part means. Preserve the original label throughout. This example builds on Unit 02’s functions, returned values and lapply().
Split a small example
labels <- c(" Riverdale, District",
"Hillford, State capital, Urban district",
"Cedar City")
parts <- strsplit(trimws(labels), ",", fixed = TRUE)
parts
trimws() removes leading and trailing whitespace. strsplit() returns a list because labels can contain different numbers of parts. fixed = TRUE treats the comma as a literal delimiter. For example, the first label has two parts, the second three, and the last only one.
parts <- lapply(parts, trimws)
place <- vapply(parts, function(x) x[1], character(1))
descriptors <- lapply(parts, function(x) x[-1])
place
lengths(descriptors)
lapply() applies trimws() to each list element. vapply() requests one character value from each element: its first part. x[-1] retains the remaining parts; the last label has no descriptor, rather than a known administrative type.
Recognize only documented categories
known_types <- c("District", "Urban district")
admin_unit <- vapply(descriptors, function(x) {
found <- intersect(x, known_types)
if (length(found) == 1L) found else NA_character_
}, character(1))
admin_unit
The first two labels identify their type explicitly. Cedar City remains unresolved: a place name containing “City” is not evidence of its legal status. State capital is an additional descriptor; it does not replace Urban district.
For real regional data, use documented source classifications and dates. Do not assign every unresolved label to the same category. Retain the other descriptors and report cases that require checking.
Package a repeated operation
A function names a reusable operation and makes its input explicit:
split_label <- function(x) {
strsplit(trimws(x), ",", fixed = TRUE)
}
split_label(labels)
Save a function definition in an .R file and load it with source("Scripts/region_helpers.R") after creating that file in your project. The crop assignment asks you to develop your own reusable region-cleaning function; this small example shows how a definition and a call fit together.