Melt Function Inconsistency with reshape2 Version

[dardesta]

I have a transpose function that imitates the arguments used in SAS.

transpose = function(input, by, var){
melt(input, id.vars = by, measure.vars=var)
}

Function Call

transpose(myData, by="Year")

This function works if myData is a data frame, but it returns an error if myData is a data table.

Error in melt.data.table(input, id.vars = by, measure.vars = var) :
argument "var" is missing, with no default

This will work if I default var to a NULL value, but then the data frame version will result in an error.

My question is: Is there a reason for the inconsistency? It would be nice to have melt.data.table suppor missing arguments so that there is not a need for the programmer to check the class of myData.

[arunsrinivasan]

@dardesta, thanks for the report. But, could you please provide a minimal reproducible example - what's myData, var, by etc..? So that I can try to reproduce the issue. Thanks.

[dardesta]

Sure. I'll use the data.table example.

library(reshape2)
library(data.table)

DF = data.frame(x=rep(c("a","b","c"),each=3), y=c(1,3,6), v=1:9)
DT = data.table(x=rep(c("a","b","c"),each=3), y=c(1,3,6), v=1:9)

transpose = function(input, by, var, id, varName="variable", valueName="value"){
    melt(input, id.vars = by, measure.vars=var)
}

#Data frame test
transpose(DF, by="x")
transpose(DF)

#Data table test
transpose(DT, by="x")
transpose(DT)

[arunsrinivasan]

@dardesta, great example! Thanks. Was easy enough to fix now (although just to be consistent with melt.data.frame). Will commit soon.