How to return dataframe with columns being lists using Rcpp?

As outlined here dataframes can have lists as columns. I try to do the same in Rcpp but without success.

df = data.frame(a=seq(1,2))
df$b = list(seq(1,10), seq(11,20))
df

My corresponding Rcpp example converts the resulting dataframe to a list (i.e. drops the dataframe attribute) - unintentionally:

cppFunction('
DataFrame testme() {
    DataFrame df = DataFrame::create(Named("a") = seq(1, 2));
    df["b"] = List::create(seq(1,10), seq(11,20));
    return df;
}')
testme()

Any ideas?

Solution 1:

I found a workaround based on this post:

cppFunction('
DataFrame testme1() {
    DataFrame df = DataFrame::create(Named("a") = seq(1, 2));
    df["b"] = List::create(seq(1,10), seq(11,20));
    df.attr("class") = "data.frame";
    df.attr("row.names") = Rcpp::seq(1, 2);
    return df;
}')
testme1()

I have to explicitly (re-)set the dataframe attribute after adding the list column to the dataframe.