A data frame is said to be folded when some cells contain
multiple elements. These are often encode as a semi-colon
separated character , such as "a;b". This function will
transform the data frame to that "a" and "b" are split and
recorded across two lines.
The simple example below illustrates a trivial case, where the table below
| X | Y |
| 1 | a;b |
| 2 | c |
is unfolded based on the Y variable and becomes
| X | Y |
| 1 | a |
| 1 | b |
| 2 | c |
where the value 1 of variable X is now duplicated.
If there is a second variable that follows the same pattern as the one used to unfold the table, it also gets unfolded.
| X | Y | Z |
| 1 | a;b | x;y |
| 2 | c | z |
becomes
| X | Y | Z |
| 1 | a | x |
| 1 | b | y |
| 2 | c | z |
because it is implied that the element in "a;b" are match to "x;y" by their respective indices. Note in the above example, unfolding by Y or Z produces the same result.
However, the following table unfolded by Y
| X | Y | Z |
| 1 | a;b | x;y |
| 2 | c | x;y |
produces
| X | Y | Z |
| 1 | a | x;y |
| 1 | b | x;y |
| 2 | c | x;y |
because "c" and "x;y" along the second row don't match. In this case, unfolding by Z would produce a different result. These examples are also illustrated below.
Note that there is no foldDataFrame() function. See
reduceDataFrame() and expandDataFrame() to flexibly encode and
handle vectors of length > 1 within cells.
unfoldDataFrame(x, k, split = ";")A DataFrame or data.frame to be unfolded.
character(1) referring to a character variable in x,
that will be used to unfold x.
character(1) passed to strsplit() to split
x[[k]].
A new object unfolded object of class class(x) with
numbers of rows >= nrow(x) and columns identical to x.
(x0 <- DataFrame(X = 1:2, Y = c("a;b", "c")))
#> DataFrame with 2 rows and 2 columns
#> X Y
#> <integer> <character>
#> 1 1 a;b
#> 2 2 c
unfoldDataFrame(x0, "Y")
#> DataFrame with 3 rows and 2 columns
#> X Y
#> <integer> <character>
#> 1 1 a
#> 2 1 b
#> 3 2 c
(x1 <- DataFrame(X = 1:2, Y = c("a;b", "c"), Z = c("x;y", "z")))
#> DataFrame with 2 rows and 3 columns
#> X Y Z
#> <integer> <character> <character>
#> 1 1 a;b x;y
#> 2 2 c z
unfoldDataFrame(x1, "Y")
#> DataFrame with 3 rows and 3 columns
#> X Y Z
#> <integer> <character> <character>
#> 1 1 a x
#> 2 1 b y
#> 3 2 c z
unfoldDataFrame(x1, "Z") ## same
#> DataFrame with 3 rows and 3 columns
#> X Y Z
#> <integer> <character> <character>
#> 1 1 a x
#> 2 1 b y
#> 3 2 c z
(x2 <- DataFrame(X = 1:2, Y = c("a;b", "c"), Z = c("x;y", "x;y")))
#> DataFrame with 2 rows and 3 columns
#> X Y Z
#> <integer> <character> <character>
#> 1 1 a;b x;y
#> 2 2 c x;y
unfoldDataFrame(x2, "Y")
#> DataFrame with 3 rows and 3 columns
#> X Y Z
#> <integer> <character> <character>
#> 1 1 a x;y
#> 2 1 b x;y
#> 3 2 c x;y
unfoldDataFrame(x2, "Z") ## different
#> DataFrame with 4 rows and 3 columns
#> X Y Z
#> <integer> <character> <character>
#> 1 1 a;b x
#> 2 1 a;b y
#> 3 2 c x
#> 4 2 c y