append two dataframes and pad with missing

append_padded

using DataFrames

function append_padded(df1,df2)
    result = DataFrame()
    for col in names(df1)
        new_col = nothing
        if in(col, names(df2))
            # vcat takes care of promoting to Union{Missing,T}
            new_col = vcat(df1[col], df2[col])
        else
            new_col = vcat(df1[col], missings(size(df2,1)))
        end
        result[col] = new_col
    end
    for col in setdiff(names(df2),names(df1))
        new_col = vcat(missings(size(df1,1)),df2[col])
        result[col] = new_col
    end
    return result
end

df = DataFrame(a=[1,2,3], b=[1., 2., 3.])
ef = DataFrame(a=[4,5], c=["s1","s2"])

r = append_padded(df,ef)