Ability to explicitly pass index names in melt.data.table measure.vars argument #4027
Description
Currently melt with multiple melting patterns works as expected only when data has a regular grid pattern. If some of the variables are missing the order of the output is scrambled.
For example:
(dt <- data.table(id = 1, a.1 = 1, a.3 = 3, b.1 = 1, b.2 = 2, b.3 = 3))
## id a.1 a.3 b.1 b.2 b.3
## 1: 1 1 3 1 2 3
melt.data.table(dt, "id" , measure.vars = list(a = 2:3, b = 4:6), variable.name = "ix")
## id ix a b
## 1: 1 1 1 1
## 2: 1 2 3 2
## 3: 1 3 NA 3But what I really want is the ix of a.3 to be 3, not 2.
## id ix a b
## 1: 1 1 1 1
## 2: 1 2 NA 2
## 3: 1 3 3 3I was hoping that explicit index names in the measure.vars would be taken into account but they are currently not:
melt.data.table(dt, "id" ,
measure.vars = list(a = c("1" = 2, "3" = 3),
b = c("4" = 4, "5" = 5, "6" = 6)),
variable.name = "ix")
## id ix a b
## 1: 1 1 1 1
## 2: 1 2 3 2
## 3: 1 3 NA 3I am fairly confident that this is related (or maybe even the same as #1739) but the example and discussion there is a bit cryptic.
Would you consider adding the ability to explicitly pass index names?
Thanks!
Details
R Under development (unstable) (2019-08-06 r76924)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.3 LTS
Matrix products: default
BLAS: /home/vspinu/bin/R-latest/lib/libRblas.so
LAPACK: /home/vspinu/bin/R-latest/lib/libRlapack.so
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8 LC_MONETARY=de_DE.UTF-8 LC_MESSAGES=C LC_PAPER=de_DE.UTF-8 LC_NAME=C LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=de_DE.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics utils datasets grDevices methods base
other attached packages:
[1] data.table_1.12.4
loaded via a namespace (and not attached):
[1] compiler_3.7.0