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Mutable dynamic data structures for R
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Ideas for mutable, dynamic frames Mutability achieved by storing columns in environments Dynamic frames achieved through active bindings in environment All sorts of cool things can be built on this, like proxies. Methods: Extraction: [[, [, $ Sub-assignment: [[<-, $<-, [<- Combination: cbind, rbind Accessors: dimnames, dim Subset: subset, head, tail, na.* Aggregation: aggregate, xtabs Transform: transform Apply: by, lapply Split: split Coercion: as.data.frame Summary: summary Duplicates: duplicated, anyDuplicated Display: print The methods that would return another frame could return a proxy, or a rooted frame. The methods [, c/rbind, subset, head, tail, transform, aggregate, and split fall into this category. Particularly with subsetting methods, one may want to delete the original frame, rather than proxy it. Passing 'drop = TRUE' to [, for example, could root the frame. We can add the 'drop' argument on to our other methods, like subset.data.frame does. There can be a function could be used to explictly root a proxy. For the subassign functions, we cannot create a new proxy, for reasons inherent in the language. But how do we decide if the modification happens at the proxy or the root? This is like <- vs. <<-. Given the mutable nature of the design, we should probably take the <<- route. Follow the parent links until the definition is found, and replace it. This requires a reverse pipeline. Transformations need to reverse transform (if possible) any assignment. We should probably just throw an error when reversal is impossible. Being an environment gives us with(), modeling functions, etc, for free The model could record the call that constructed it, which would allow displaying the workflow or "pipeline" behind it Would also be nice if something provided a Qt data model on top of it The next step is to figure out change notification. Handlers need to be registered, with two arguments, i and j, that index into the rows and columns, respectively. Any replacement function will necessarily modify the frame in-place, and the change event will be emitted. Parameters of dynamic columns can of course be changed through the use of closures, but the frame must be explicitly informed of the change. Every binding will need to be active, so that when a change is made, an event is reported. Event reporting will need to be frozen when many changes are about to be made. When frozen, the events are aggregated. When the thaw method is called, the aggegated event is dispatched. Each frame will need to listen to each of its parents/components and forward the events. Some stages may need to add more changes. For example, a subset() stage will check if its subsetting has changed and, if so, add all columns to the event. A transform() frame would report changes to any transformed columns, if not already marked.