How to order descending in @orderby?

[ferris-wufei]

Tried adding a minus sign before the column symbol, but got the error msg

MethodError: no method matching -(::String)
...

Is there any workaround? Thanks.

[nalimilan]

Unfortunately that doesn't seem to be supported currently. However it shouldn't be hard to support, by adding a keyword argument and passing it to sortperm.

[tshort]

It works for me:

julia> using DataFrames, DataFramesMeta

julia> d = DataFrame(n = 1:20, x = [3, 3, 3, 3, 1, 1, 1, 2, 1, 1,
                                           2, 1, 1, 2, 2, 2, 3, 1, 1, 2]);

julia> @orderby(d, -:x)
20×2 DataFrames.DataFrame
│ Row │ n  │ x │
├─────┼────┼───┤
│ 1   │ 1  │ 3 │
│ 2   │ 2  │ 3 │
│ 3   │ 3  │ 3 │
│ 4   │ 4  │ 3 │
│ 5   │ 17 │ 3 │
│ 6   │ 8  │ 2 │
│ 7   │ 11 │ 2 │
│ 8   │ 14 │ 2 │
│ 9   │ 15 │ 2 │
│ 10  │ 16 │ 2 │
│ 11  │ 20 │ 2 │
│ 12  │ 5  │ 1 │
│ 13  │ 6  │ 1 │
│ 14  │ 7  │ 1 │
│ 15  │ 9  │ 1 │
│ 16  │ 10 │ 1 │
│ 17  │ 12 │ 1 │
│ 18  │ 13 │ 1 │
│ 19  │ 18 │ 1 │
│ 20  │ 19 │ 1 │

julia> g = groupby(d, :x);

julia> @orderby(g, -mean(:n))
DataFrames.GroupedDataFrame  3 groups with keys: Symbol[:x]
First Group:
6×2 DataFrames.SubDataFrame{Array{Int64,1}}
│ Row │ n  │ x │
├─────┼────┼───┤
│ 1   │ 8  │ 2 │
│ 2   │ 11 │ 2 │
│ 3   │ 14 │ 2 │
│ 4   │ 15 │ 2 │
│ 5   │ 16 │ 2 │
│ 6   │ 20 │ 2 │
⋮
Last Group:
5×2 DataFrames.SubDataFrame{Array{Int64,1}}
│ Row │ n  │ x │
├─────┼────┼───┤
│ 1   │ 1  │ 3 │
│ 2   │ 2  │ 3 │
│ 3   │ 3  │ 3 │
│ 4   │ 4  │ 3 │
│ 5   │ 17 │ 3 │

[nalimilan]

I guess that only works for numeric columns...

[tshort]

Correct on numeric. One way around that might be to encode with a CategoricalArray and control the sort order with that. (I didn't try that.)

Or, someone could PR the use of a KW arg to add this feature.

[pdeffebach]

Closed in favor of #166