This isn't at all an urgent practical question, but recently while exploring the details of how R formulas are interpreted, I learned of this funny special case for how / interacts with +. In all of the following cases, the multiplication-like operator simply distributes over addition: (a + b):c = a:c + a:c a:(b + c) = a:b + a:c (a + b)*c = a*c + b*c a*(b + c) = a*b + a*c a/(b + c) = a/b + a/c
But: (a + b)/c = a + b + a:b:c, not a/c + b/c = a + a:c + b + b:c Chambers and Hastie mention this, but give no explanation (page 29/30, "Slightly more subtle is..."). So for my own edification, does anyone know/care to speculate about why (a + b)/c works this way? -- Nathaniel ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
