Efficient transpose of list
transpose.Rd
transpose
is an efficient way to transpose lists
, data.frames
or data.tables
.
Arguments
- l
A list, data.frame or data.table.
- fill
Default is
NA
. It is used to fill shorter list elements so as to return each element of the transposed result of equal lengths.- ignore.empty
Default is
FALSE
.TRUE
will ignore length-0 list elements.- keep.names
The name of the first column in the result containing the names of the input; e.g.
keep.names="rn"
. By defaultNULL
and the names of the input are discarded.- make.names
The name or number of a column in the input to use as names of the output; e.g.
make.names="rn"
. By defaultNULL
and default names are given to the output columns.- list.cols
Default is
FALSE
.TRUE
will avoid promoting types and return columns of typelist
instead.factor
will always be cast tocharacter
.
Details
The list elements (or columns of data.frame
/data.table
) should be all atomic
. If list elements are of unequal lengths, the value provided in fill
will be used so that the resulting list always has all elements of identical lengths. The class of input object is also preserved in the transposed result.
The ignore.empty
argument can be used to skip or include length-0 elements.
This is particularly useful in tasks that require splitting a character column and assigning each part to a separate column. This operation is quite common enough that a function tstrsplit
is exported.
factor
columns are converted to character
type. Attributes are not preserved at the moment. This may change in the future.
Value
A transposed list
, data.frame
or data.table
.
list
outputs will only be named according to make.names
.
Examples
ll = list(1:5, 6:8)
transpose(ll)
#> [[1]]
#> [1] 1 6
#>
#> [[2]]
#> [1] 2 7
#>
#> [[3]]
#> [1] 3 8
#>
#> [[4]]
#> [1] 4 NA
#>
#> [[5]]
#> [1] 5 NA
#>
setDT(transpose(ll, fill=0))[]
#> V1 V2 V3 V4 V5
#> <int> <int> <int> <int> <int>
#> 1: 1 2 3 4 5
#> 2: 6 7 8 0 0
DT = data.table(x=1:5, y=6:10)
transpose(DT)
#> V1 V2 V3 V4 V5
#> <int> <int> <int> <int> <int>
#> 1: 1 2 3 4 5
#> 2: 6 7 8 9 10
DT = data.table(x=1:3, y=c("a","b","c"))
transpose(DT, list.cols=TRUE)
#> V1 V2 V3
#> <list> <list> <list>
#> 1: 1 2 3
#> 2: a b c
# base R equivalent of transpose
l = list(1:3, c("a", "b", "c"))
lapply(seq(length(l[[1]])), function(x) lapply(l, `[[`, x))
#> [[1]]
#> [[1]][[1]]
#> [1] 1
#>
#> [[1]][[2]]
#> [1] "a"
#>
#>
#> [[2]]
#> [[2]][[1]]
#> [1] 2
#>
#> [[2]][[2]]
#> [1] "b"
#>
#>
#> [[3]]
#> [[3]][[1]]
#> [1] 3
#>
#> [[3]][[2]]
#> [1] "c"
#>
#>
transpose(l, list.cols=TRUE)
#> [[1]]
#> [[1]][[1]]
#> [1] 1
#>
#> [[1]][[2]]
#> [1] "a"
#>
#>
#> [[2]]
#> [[2]][[1]]
#> [1] 2
#>
#> [[2]][[2]]
#> [1] "b"
#>
#>
#> [[3]]
#> [[3]][[1]]
#> [1] 3
#>
#> [[3]][[2]]
#> [1] "c"
#>
#>
ll = list(nm=c('x', 'y'), 1:2, 3:4)
transpose(ll, make.names="nm")
#> $x
#> [1] 1 3
#>
#> $y
#> [1] 2 4
#>