Writing Functions/Macros with TidierDB Chains

How can functions pass arguments to a TidierDB chain?

In short, you have to use a macro instead in conjuction with @interpolate

Setting up the macro

To write a macro that will take arguments and pass them to a TidierDB chain, there are 3 steps:

1. Write macro with the desired argument(s), and, after the quote, add the chain. Arguments to be changed/interpolated must be prefixed with !!
2. Use @interpolate to make these arguemnts accessible to the chain. @interpolate takes touples as argument (one for the !!name, and one for the actual content you want the chain to use)
3. Run @interpolate and then the chain macro sequentially

using TidierDB
db = connect(duckdb())
path = "https://gist.githubusercontent.com/seankross/a412dfbd88b3db70b74b/raw/5f23f993cd87c283ce766e7ac6b329ee7cc2e1d1/mtcars.csv"
copy_to(db, path, "mtcars");

# STEP 1
macro f1(conditions, columns) # The arguemnt names will be names of the `!!` values
    return quote
    # add chain here
      @chain db_table(db, :mtcars) begin
           @filter(!!conditions > 3)
           @select(!!columns)
           @aside @show_query _
           @collect
         end # ends the chain
    end # ends the quote.
end # ends the macro

# STEP 2
variable = :gear;
cols = [:model, :mpg, :gear, :wt];
@interpolate((conditions, variable), (columns, cols));
@f1(variable, cols)

17×4 DataFrame
 Row │ model           mpg       gear    wt
     │ String?         Float64?  Int32?  Float64?
─────┼────────────────────────────────────────────
   1 │ Mazda RX4           21.0       4     2.62
   2 │ Mazda RX4 Wag       21.0       4     2.875
   3 │ Datsun 710          22.8       4     2.32
  ⋮  │       ⋮            ⋮        ⋮        ⋮
  15 │ Ferrari Dino        19.7       5     2.77
  16 │ Maserati Bora       15.0       5     3.57
  17 │ Volvo 142E          21.4       4     2.78
                                   11 rows omitted

Lets say you wanted to filter on new variable with a different name and select new columns,

new_condition = :wt;
new_cols = [:model, :drat]
@interpolate((conditions, new_condition), (columns, new_cols));
@f1(new_condition, new_cols)

20×2 DataFrame
 Row │ model              drat
     │ String?            Float64?
─────┼─────────────────────────────
   1 │ Hornet 4 Drive         3.08
   2 │ Hornet Sportabout      3.15
   3 │ Valiant                2.76
  ⋮  │         ⋮             ⋮
  18 │ Pontiac Firebird       3.08
  19 │ Ford Pantera L         4.22
  20 │ Maserati Bora          3.54
                    14 rows omitted

You can also interpolate vectors of strings into a @filter(col in (values)) as well by using the following syntax @filter(col in [!!values])

In short, the first argument in @interpolate must be the name of the macro argument it refers to, and the second argument is what you would like to replace it.

We recognize this adds friction and that it is not ideal, but given the TidierDB macro expressions/string interplay, this is currently the most graceful and functional option available and hopefully a temporary solution to better interpolation that mirrors TidierData.jl.

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