Benjamin Schmidt

Thanks for your explanation about how to use external variables! I'm interested if you have more resources on the recommended ways to manage external variables in the operations. I also had seen https://uwdata.github.io/arquero/api/#addFunction, but I could not make it work.

Sylvain Lesage

Since writing this, I've come to see that the recommend way is to bind parameters to the table, which are then available for computation through a special variable inside functions $.
Defining separate ops is also possible, but not always necessary.

So for instance, given

my_name = "Wesleyan University"

then 

table.filter(d => op.equal(d.INSTNM, my_name)).view()

will not work, but

table.params({name: my_name}).filter((d, $) => op.equal(d.INSTNM, $.name)).view()

works nicely!

Thanks a lot! It's much easier to think about for me, even if the other way is also elegant.

Adding to the conversation for anyone else researching this issue; as detailed [in this forum discussion](https://talk.observablehq.com/t/dynamic-rollup-object-for-arquero/4721).

I've encountered a [use case](https://observablehq.com/@mariodelgadosr/dow-jones-industrial-average-correlation-analysis-with-ar#rollupObj) where the only alternative was to use the [eval](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval) method to dynamically create the properties for data-driven rollup processing.

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