Unlists Columns of Lists by Combinations of Values

Unlists columns of lists by row creating combinations of values in the process.

list_unlister(indt, addRN = TRUE)

Arguments

indt	The input data.table. The input can also be a list, possibly with elements of different lengths.
addRN	Logical. Should a column named "rn" be added to the data.table? Such a column is required, so if it does not already exist, it is suggested to keep this set to TRUE, the default.

Value

A data.table.

References

http://stackoverflow.com/q/23217958/1270695

Author

Ananda Mahto

Examples

L1 <- list(list("A", c("B", "C")), list(1:2, 1:3))
list_unlister(L1)
#>    rn V1 V2
#> 1:  1  A  1
#> 2:  1  A  2
#> 3:  2  B  1
#> 4:  2  C  1
#> 5:  2  B  2
#> 6:  2  C  2
#> 7:  2  B  3
#> 8:  2  C  3

## Note the NULLs and the shorter length of the first list item
L2 <- list(V1 = list("A", c("A", "B"), "X", NULL),
V2 = list(1, c(1, 2, 3), c(1, 2), c(1, 2, 3, 4), 1),
V3 = list(c("a", "b"), "c", "d", c("e", "f"), c("g", "h", "i")))
list_unlister(L2)
#>     rn   V1 V2 V3
#>  1:  1    A  1  a
#>  2:  1    A  1  b
#>  3:  2    A  1  c
#>  4:  2    B  1  c
#>  5:  2    A  2  c
#>  6:  2    B  2  c
#>  7:  2    A  3  c
#>  8:  2    B  3  c
#>  9:  3    X  1  d
#> 10:  3    X  2  d
#> 11:  4 <NA>  1  e
#> 12:  4 <NA>  2  e
#> 13:  4 <NA>  3  e
#> 14:  4 <NA>  4  e
#> 15:  4 <NA>  1  f
#> 16:  4 <NA>  2  f
#> 17:  4 <NA>  3  f
#> 18:  4 <NA>  4  f
#> 19:  5 <NA>  1  g
#> 20:  5 <NA>  1  h
#> 21:  5 <NA>  1  i
#>     rn   V1 V2 V3

DT <- data.table::data.table(
x1 = list("A", c("A", "B"), "X", NULL, c("Z", "W")),
x2 = list(1, c(1, 2, 3), c(1, 2), c(1, 2, 3, 4), 1),
x3 = list(c("a", "b"), "c", "d", c("e", "f"), c("g", "h", "i")))
list_unlister(DT)
#>     rn   x1 x2 x3
#>  1:  1    A  1  a
#>  2:  1    A  1  b
#>  3:  2    A  1  c
#>  4:  2    B  1  c
#>  5:  2    A  2  c
#>  6:  2    B  2  c
#>  7:  2    A  3  c
#>  8:  2    B  3  c
#>  9:  3    X  1  d
#> 10:  3    X  2  d
#> 11:  4 <NA>  1  e
#> 12:  4 <NA>  2  e
#> 13:  4 <NA>  3  e
#> 14:  4 <NA>  4  e
#> 15:  4 <NA>  1  f
#> 16:  4 <NA>  2  f
#> 17:  4 <NA>  3  f
#> 18:  4 <NA>  4  f
#> 19:  5    Z  1  g
#> 20:  5    W  1  g
#> 21:  5    Z  1  h
#> 22:  5    W  1  h
#> 23:  5    Z  1  i
#> 24:  5    W  1  i
#>     rn   x1 x2 x3