Column-wise macros

Column-wise macros allow using symbols instead of columns. The order of the arguments is always the same: the first argument is the table and the last argument is the expression (can be a begin ... end block). If the table is omitted, the macro is automatically curried (useful for piping).

Shared features across all row-wise macros:

Symbols refer to fields of the row.
_ refers to the whole table.
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.
An optional grouping argument is allowed: see Column-wise macros with grouping argument
Out-of-core tables are not supported out of the box, except when grouping

Replace symbols with columns

JuliaDBMeta.@with — Macro.

@with(d, x)

Replace all symbols in expression x with the respective column in d. In this context, _ refers to the whole table d. To use actual symbols, escape them with ^, as in ^(:a). Use cols(c) to refer to column 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 = ["x","y","z"]));

julia> @with t mean(:a)
2.0

julia> @with t mean(:a)*length(_)
6.0

julia> @with t join(:b)
"xyz"

julia> @with t @show ^(:a) != :a
:a != getfield(JuliaDBMeta.columns(t), :a) = true
true

julia> c = :a
:a

julia> @with t cols(c)
3-element Array{Int64,1}:
 1
 2
 3

Note that you can use this syntax to modify columns in place as well:

julia> @with t :b .= :b .* string.(:a)
3-element Array{String,1}:
 "x1"
 "y2"
 "z3"

julia> t
Table with 3 rows, 2 columns:
a  b
───────
1  "x1"
2  "y2"
3  "z3"

source

Add or modify a column

JuliaDBMeta.@transform_vec — Macro.

@transform_vec(d, x)

Replace all symbols in expression x with the respective column in d: the result has to be a NamedTuple of vectors or a table and is horizontally merged with d. In this context, _ refers to the whole table d. To use actual symbols, escape them with ^, as in ^(:a). Use {} syntax for automatically named NamedTuples. Use cols(c) to refer to column 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 = ["x","y","z"]));

julia> @transform_vec t {:a .+ 1}
Table with 3 rows, 3 columns:
a  b    a .+ 1
──────────────
1  "x"  2
2  "y"  3
3  "z"  4

source

Select data

JuliaDBMeta.@where_vec — Macro.

@where_vec(d, x)

Replace all symbols in expression x with the respective column in d: the result has to be an Array of booleans which is used to get a view of d. In this context, _ refers to the whole row. To use actual symbols, escape them with ^, as in ^(:a). The result has to be a NamedTuple of vectors or a table and is horizontally merged with d. Use {} syntax for automatically named NamedTuples. Use cols(c) to refer to column 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 = ["x","y","z"]));

julia> @where_vec t (:a .>= 2) .& (:b .!= "y")
Table with 1 rows, 2 columns:
a  b
──────
3  "z"

source