Using formulae to set gpar attributes

[gvegayon]

Right now we do have a function to parse formulas for edge colors, but ideally, we could have a more comprehensive/flexible system to parse formulas and return various types of outcomes.

About the input

• Formulas for mixing ego/alter attributes.
• Formulas for using either ego or alter attributes.
• Formulas using edge attributes.

Mixing these three should be relatively straightforward. Since at the edge level, we will only find one attribute of each.

The problem is when, for example, we would like to generate a statistic at the ego-network level.

About the output

• Formulas should return numbers/factors:
  • Integers (factors)
  • Fractions
  • Strings
  • Etc.

This could follow a goal similar to what the scales R package does, this is, return palettes/functions for plots.