Split a data frame z into two data frames x and y so
that merge(x, y) is z.
Arguments
- z
data frame
- by
vector of names of columns in
zthat are used to build groups of rows ofzso 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 framexwhereas the remaining columns will appear in the data frameyof 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"))
#> $x
#> name age height
#> 1 peter 42 181
#> 3 paul 31 178
#> 4 mary 28 172
#>
#> $y
#> name subject year mark
#> 1 peter maths 2016 A
#> 2 peter bio 2017 B
#> 3 paul bio 2017 B
#> 4 mary bio 2017 A
#> 5 paul chem 2015 C
#> 6 mary maths 2016 b
#>
# 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"))
#> $x
#> subject year
#> 1 maths 2016
#> 2 bio 2017
#> 5 chem 2015
#>
#> $y
#> subject name age height mark
#> 1 maths peter 42 181 A
#> 2 bio peter 42 181 B
#> 3 bio paul 31 178 B
#> 4 bio mary 28 172 A
#> 5 chem paul 31 178 C
#> 6 maths mary 28 172 b
#>
# Test if merge(result$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
#> [1] TRUE
identical(fullySorted(z[, columns]), fullySorted(y2[, columns])) # TRUE
#> [1] TRUE