min/max on differences of DataFrame columns in Julia

[cocoandmore]

When I try to retrieve the maximums of differences of columns in a DataFrame I get an error. What is wrong?

using DataFrames

a = [2,4,10,4,8,8]
b = [5,9,7,2,8,7]
c = [2,9,7,6,8,1]

df = DataFrame(A = a, B = b, C = c)
df[2,:A] = NA
df[3,:C] = NA

ab=df[:A] - df[:B]
bc=df[:B] - df[:C]
ac=df[:A] - df[:C]

df[:max] = max(ab, bc, ac)

println(df)

=> LoadError: MethodError: no method matching isless(::DataArrays.DataArray{Int64,1}, ::Array{Any,1})

Doing the maximum of either df[:max] = max(ab, bc) or df[:max] = max(a, b, c) works as expected.

Can anybody clarify what's going on? Thank you!

[nalimilan]

Thanks for the report. Sounds like a bug in DataArrays, which is going to be deprecated. Anyway the recommended syntax is now df[:max] = max.(ab, bc, ac), and AFAICT it works both with 0.8.4 and git master (at least after JuliaStats/NullableArrays.jl#166).