JLD experiments with DataFrames

Here is an extension to JLD to try to support reading of DataFrames. Writing seems to be okay.

import HDF5.read, JLD.JldFile, JLD.getrefs

function read{D<:AbstractDataFrame}(obj::HDF5Dataset{JldFile}, ::Type{D})
    kv = getrefs(obj, Any)
    keys = kv[1]
    vals = kv[2]
    d = D()
    for (k,v) in zip(keys, vals)
        d[k] = v
    end
    d
end

Here is an example of use:

julia> d = {:a => [1:5], :b => pi*[2:6]}
{:b=>[6.28319, 9.42478, 12.5664, 15.708, 18.8496],:a=>[1, 2, 3, 4, 5]}

julia> df = DataFrame({[2:6], pi*[1:5]})   # arrays only
5x2 DataFrame:
        x1      x2
[1,]     2 3.14159
[2,]     3 6.28319
[3,]     4 9.42478
[4,]     5 12.5664
[5,]     6  15.708

julia> df2 = @DataFrame(a => [1:5], b => pi * [1:5])   # DataArray columns
5x2 DataFrame:
        a       b
[1,]    1 3.14159
[2,]    2 6.28319
[3,]    3 9.42478
[4,]    4 12.5664
[5,]    5  15.708

julia> file = jldopen("mydata.jld", "w")
Julia data file version 0.0.1: mydata.jld

julia> write(file, "d", d)

julia> write(file, "df", df)

julia> write(file, "df2", df2)

julia> close(file)

julia> file = jldopen("mydata.jld", "r")
Julia data file version 0.0.1: mydata.jld

julia> x = read(file, "d")
{:b=>[6.28319, 9.42478, 12.5664, 15.708, 18.8496],:a=>[1, 2, 3, 4, 5]}

julia> x = read(file, "df")
HDF5-DIAG: Error detected in HDF5 (1.8.4-patch1) thread 139749181699904:
  #000: ../../../src/H5A.c line 546 in H5Aopen(): unable to load attribute info from object header
    major: Attribute
    minor: Unable to initialize object
  #001: ../../../src/H5Oattribute.c line 533 in H5O_attr_open_by_name(): can't locate attribute
    major: Attribute
    minor: Object not found
HDF5-DIAG: Error detected in HDF5 (1.8.4-patch1) thread 139749181699904:
  #000: ../../../src/H5A.c line 1385 in H5Aget_name(): not an attribute
    major: Invalid arguments to routine
    minor: Inappropriate type
ERROR: Error getting attribute name
 in h5a_get_name at /home/tshort/.julia/HDF5/src/plain.jl:1699
 in h5a_get_name at /home/tshort/.julia/HDF5/src/plain.jl:1749
 in h5a_open at /home/tshort/.julia/HDF5/src/plain.jl:1699
 in a_read at /home/tshort/.julia/HDF5/src/plain.jl:922
 in read at /home/tshort/.julia/HDF5/src/jld.jl:330
 in read at /home/tshort/.julia/HDF5/src/jld.jl:176
 in read at /home/tshort/.julia/HDF5/src/plain.jl:934


julia> read(file["df"], DataFrame)   # works for Array columns
5x2 DataFrame:
        x1      x2
[1,]     2 3.14159
[2,]     3 6.28319
[3,]     4 9.42478
[4,]     5 12.5664
[5,]     6  15.708


julia> read(file["df2"], DataFrame)   # broken for DataArray columns
ERROR: no method start(Symbol,)
 in read at /home/tshort/.julia/HDF5/src/jld.jl:333
 in read at /home/tshort/.julia/HDF5/src/jld.jl:176
 in getrefs at /home/tshort/.julia/HDF5/src/jld.jl:358
 in read at /home/tshort/.julia/HDF5/src/jld.jl:302
 in read at /home/tshort/.julia/HDF5/src/jld.jl:176
 in getrefs at /home/tshort/.julia/HDF5/src/jld.jl:358
 in read at /tmp/julia_eval_region.jl:4

tshort/testing.md