Best way to "replace" data?

[jonathancallahan]

It is my impression that tables are designed to be immutable. If you want something different, apply some verbs and .reify() if needed. What I want is something that feels like a "replace" verb.

My simple use case is that I would like to modify incoming data by lifting up negative values to zero.

I'm wondering if there is a better way than the following, which won't work when the incoming columns are unknown:

aq.table({
    'a': [1,2,3,-1],
    'b': [7,8,-1,9]
  })
  .derive({
    a: d => d.a < 0 ? 0 : d.a,
    b: d => d.b < 0 ? 0 : d.b,
  })
  .print();

[jonathancallahan]

After wrapping my head around Table Expressions, I came up with the following solution for my issue:

negativeToZero = function(dt) {
  // Programmatically create a values object that replaces values
  const ids = dt.columnNames();
  let values = {}
  ids.map(id => values[id] = "d => d['" + id + "'] <= 0 ? 0 : d['" + id + "']");
  // Create and return the dt with all negative values replaced
  let new_dt = dt.derive(values);
  return(new_dt)
}

This isn't built as table method but it gets the job done.

let dt = aq.table({
    'a': [1,2,3,-1],
    'b': [7,8,-1,9]
  })

negativeToZero(dt).print();