Selection
Experimentally, there is a new macro to simplify the creation of selector objects:
JuliaDBMeta.@=>
— Macro.@=>(expr...)
Create a selector based on expressions expr
. Symbols are used to select columns and infer an appropriate anonymous function. In this context, _
refers to the whole row. To use actual symbols, escape them with ^
, as in ^(:a)
. Use cols(c)
to refer to field c
where c
is a variable that evaluates to a symbol. c
must be available in the scope where the macro is called.
Examples
julia> t = table((a = [1,2,3], b = [4,5,6]));
julia> select(t, @=>(:a, :a + :b))
Table with 3 rows, 2 columns:
a a + b
────────
1 5
2 7
3 9
JuliaDBMeta.@select
— Macro.@select(d, x)
Short-hand for select(d, @=>(x))
Examples
julia> t = table((a = [1,2,3], b = [4,5,6]));
julia> @select(t, (:a, :a + :b))
Table with 3 rows, 2 columns:
a a + b
────────
1 5
2 7
3 9