Add join_natural method

This issue captures a missing feature that’s bothered me a little too; a quick and dirty way to join tables on shared keys as in tidyverse’s inner_join or MySQL’s NATURAL JOIN. Especially without named arguments in JS, it’s hard to remember how to do this with existing joins.

In observable I’ve started adding a join_natural function that mimics their behavior: I wonder if you’d consider adding something similar as a method.

  aq.internal.Table.prototype.join_natural = function(right) {
    const names = this.columnNames()
    return this.join(right, undefined, [names,right.columnNames().filter(d => names.indexOf(d) == -1)])
  }

Would probably be best if it threw an error if there are no shared keys. (?)

Thanks again for your work–still greatly enjoying this library’s contribution.

[jheer]

Thanks! You both convinced me to have Arquero throw an error when there are no shared columns. I’ve also updated the PR to (1) ensure proper handling of natural left, right, and full joins, and (2) suppress duplicated key column output.

The handling of full outer joins is a bit subtle. In SQL, natural full joins are not allowed. In dplyr, they are allowed but cause the “duplicate” key columns to be merged, using the value of whichever column is non-empty. I’ve followed the dplyr semantics here in Arquero when de-duplicating shared key columns in a full outer join.

[juba]

I think this would be great, and I also agree with @bmschmidt caution about the potential danger of non explicitly asked for cartesian product : I already ended several times with a hanged session in R doing these sort of things, too.