Retrieving the aggregated values of an histogram

[Malik Koné]

Hi,

How can one retrieve the aggregated values of an histogram ?

I achieved what I want in  this d3 observable notebook. On a bar click  the selected variable is updated with the bar's underlying values.

I need to replicate this in vega or vega-lite, with the documentation histogram for example.

I though using an aggregation operator or an expression but I could not find one that returned the underlying liste value.  I'm obviously not taking the right path.  Please guide me.

[Malik Koné]

I'm only able to retrieve the first value of the bin as in this chart excerpt 

[Malik Koné]

I'm looking for the inverse of `flatten`.  The closest would be the `pivot` transform with a `concat` operator.