unmerge: Invert the Merging of two Data Frames

In KWB-R/kwb.utils: General Utility Functions Developed at KWB

Invert the Merging of two Data Frames

Description

Split a data frame z into two data frames x and y so that merge(x, y) is z.

Usage

unmerge(z, by)

Arguments

z	data frame
by	vector of names of columns in z that are used to build groups of rows of z so that within each group the values in these columns do not change. For each group the columns being constant over all rows are identified. Columns that are constant in each group will appear in the data frame x whereas the remaining columns will appear in the data frame y of the returned list.

Value

list with two elements x and y each of which are data frames containing at least the columns given in by.

Examples

z <- data.frame(
  name = c("peter", "peter", "paul", "mary", "paul", "mary"),
  age = c(42, 42, 31, 28, 31, 28),
  height = c(181, 181, 178, 172, 178, 172),
  subject = c("maths", "bio", "bio", "bio", "chem", "maths"),
  year = c(2016, 2017, 2017, 2017, 2015, 2016),
  mark = c("A", "B", "B", "A", "C", "b")
)
  
# What fields seem to be properties of objects identified by name?
# -> Age and height are fix properties of the persons identified by name
(result1 <- unmerge(z, "name"))

# What fields seem to be properties of objects identified by subject?
# -> It seems that the subjects have been tested in different years
(result2 <- unmerge(z, "subject"))

# Test if merge(result$x, result$y) results in z
y1 <- merge(result1$x, result1$y)
y2 <- merge(result2$x, result2$y)

columns <- sort(names(z))

identical(fullySorted(z[, columns]), fullySorted(y1[, columns])) # TRUE
identical(fullySorted(z[, columns]), fullySorted(y2[, columns])) # TRUE

KWB-R/kwb.utils documentation built on April 1, 2024, 7:12 a.m.