On Fri, Aug 5, 2016 at 9:53 PM, Yichao Yu <[email protected]> wrote:
>
>
> On Fri, Aug 5, 2016 at 9:50 PM, Tamas Papp <[email protected]> wrote:
>
>> TL;DR: how to construct an :(a,b,c) expression from [:a,:b,:c] for use
>> in a macro.
>>
>
> julia> a = [:a, :b, :c]
> 3-element Array{Symbol,1}:
> :a
> :b
> :c
>
> julia> :($(a...))
> (:a,:b,:c)
>
Correction,
julia> :($(a...),)
:((a,b,c))
>
>
>
>>
>> Long version: I am trying to construct a macro that zips columns of
>> dataframes and then iterates & collects over them, eg something that
>> expands
>>
>> @in_dataframe(df, a+b+c, 1 => a, 2 => b, 3 => c)
>>
>> to
>>
>> [a+b+c for (a,b,c) in zip(df[1],df[2],df[3])]
>>
>> Note how indexes are values, not inferred from walking the expression,
>> as in DataFramesMeta. However, I want
>>
>> @in_dataframe(df, a+b+c, a, b, c)
>>
>> to work when column names correspond to symbols, hence the two
>> parse_colspec methods below.
>>
>> I came up with
>>
>> macro in_dataframe(df, expression, colspecs...)
>> function parse_colspec(e::Expr)
>> @assert e.head == :(=>)
>> varname = e.args[2]
>> @assert isa(varname, Symbol)
>> (varname,e.args[1])
>> end
>> function parse_colspec(varname::Symbol)
>> (varname,QuoteNode(varname))
>> end
>> dfvar = gensym("df")
>> vars = map(parse_colspec, colspecs)
>> quote
>> let $dfvar = $df
>> [$expression
>> for $(tuple(Symbol[v[1] for v in vars]...)) in
>> zip($([:($dfvar[$(v[2])]) for v in vars]...))]
>> end
>> end
>> end
>>
>> Trying
>>
>> macroexpand(:(@in_dataframe(df1, a+b+c, 1 => a, 2 => b, 3 => c)))
>>
>> looks OK, except for the (:a,:b,:c) after the "for". I can't figure out
>> how to get (a,b,c). Other hints to improve style would also be
>> appreciated.
>>
>> Regards,
>>
>> Tamas
>>
>
>
