query about the "z" in the fastshap algorithm (7)

[nicholasjhorton]

Issue relates to printed book and electronic version 2020-02-01

Section 16.8.1, Algorithm 7: https://bradleyboehmke.github.io/HOML/iml.html#shapley-values

      | b1 = x, but all the features in perm that appear after 
      |      feature xj get their values swapped with the 
      |      corresponding values in z.

What is z? It doesn't seem to be defined in the algorithm or the section.

PS Kudos for an excellent book!

[bgreenwell]

Hi @nicholasjhorton, good catch. Here, z corresponds to an instance drawn at random from the learning sample (or suitable background data set). The reference to this algorithm can be found here; in the image, z is equivalent to w. Will keep this open as a note to fix in the next print/version.