Catch some edge-case in heuristic_in_bin()

NEWS.md

@@ -2,7 +2,7 @@
 
 ## `sv_dependence()`: Control over automatic color feature selection
 
-### How is the color feature selected anyway?
+### How is the color feature selected, anyway?
 
 If no SHAP interaction values are available, by default, the color feature `v'` is selected by the heuristic `potential_interaction()`, which works as follows:
 

R/potential_interactions.R

@@ -89,12 +89,10 @@ heuristic <- function(color, s, bins, color_num, scale, adjusted) {
   if (isTRUE(color_num)) {
     color <- .as_numeric(color)
   }
-  color <- split(color, bins)
-  s <- split(s, bins)
   M <- mapply(
     heuristic_in_bin,
-    color = color,
-    s = s,
+    color = split(color, bins),
+    s = split(s, bins),
     MoreArgs = list(scale = scale, adjusted = adjusted)
   )
   stats::weighted.mean(M[1L, ], M[2L, ], na.rm = TRUE)
@@ -112,24 +110,24 @@ heuristic <- function(color, s, bins, color_num, scale, adjusted) {
 #' @returns
 #'   A (1x2) matrix with heuristic and number of observations.
 heuristic_in_bin <- function(color, s, scale = FALSE, adjusted = FALSE) {
-  suppressWarnings(
-    tryCatch(
-      {
-        z <- stats::lm(s ~ color)
-        r <- z$residuals
-        n <- length(r)
-        var_y <- stats::var(z$fitted.values + r)
-        denom <- if (adjusted) z$df.residual else n - 1
-        var_r <- sum(r^2) / denom
-        stat <- 1 - var_r / var_y
-        if (scale) {
-          stat <- stat * var_y
-        }
-        cbind(stat = stat, n = n)
-      },
-      error = function(e) return(cbind(stat = NA, n = 0))
-    )
-  )
+  ok <- !is.na(color)
+  color <- color[ok]
+  s <- s[ok]
+  n <- length(s)
+  var_s <- stats::var(s)
+  if (n < 2L || var_s < .Machine$double.eps || length(unique(color)) < 2L) {
+    return(cbind(stat = NA, n = n))
+  }
+  z <- stats::lm(s ~ color)
+  var_r <- sum(z$residuals^2) / (if (adjusted) z$df.residual else n - 1)
+  stat <- 1 - var_r / var_s
+  if (scale) {
+    stat <- stat * var_s
+  }
+  if (!is.finite(stat)) {
+    stat <- NA
+  }
+  cbind(stat = stat, n = n)
 }
 
 # Like as.numeric(), but can deal with factor variables

R/sv_dependence.R

@@ -137,8 +137,8 @@ sv_dependence.shapviz <- function(object, v, color_var = "auto", color = "#3b528
       scale = ih_scale,
       adjusted = ih_adjusted
     )
-    # 'scores' can be NULL, or a numeric vector like c(0.1, 0, -0.01, NaN, NA)
-    # Thus, let's take the first positive one (or none)
+    # 'scores' can be NULL, or a sorted vector like c(0.1, 0, -0.01, NA)
+    # Thus, let's take the first positive one (or NULL)
     scores <- scores[!is.na(scores) & scores > 0]  # NULL stays NULL
     color_var <- if (length(scores) >= 1L) names(scores)[1L]
   }

tests/testthat/test-potential_interactions.R

@@ -67,7 +67,104 @@ test_that("heuristic_in_bin() returns R-squared", {
 })
 
 test_that("Failing heuristic_in_bin() returns NA", {
-  expect_equal(heuristic_in_bin(0, 1:2), cbind(stat = NA, n = 0))
+  expect_equal(heuristic_in_bin(c(NA, NA), 1:2), cbind(stat = NA, n = 0))
+})
+
+test_that("heuristic_in_bin() returns NA for constant response", {
+  expect_equal(
+    heuristic_in_bin(color = 1:3, s = c(1, 1, 1)),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = 1:3, s = c(1, 1, 1), scale = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = 1:3, s = c(1, 1, 1), adjust = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = 1:3, s = c(1, 1, 1), adjust = TRUE, scale = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+})
+
+test_that("heuristic_in_bin() returns NA for constant color", {
+  expect_equal(
+    heuristic_in_bin(s = 1:3, color = c(1, 1, 1)),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(s = 1:3, color = c(1, 1, 1), scale = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(s = 1:3, color = c(1, 1, 1), adjust = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(s = 1:3, color = c(1, 1, 1), adjust = TRUE, scale = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+})
+
+test_that("heuristic_in_bin() returns 0 if response and color are constant", {
+  z <- c(1, 1)
+  expect_equal(
+    heuristic_in_bin(color = z, s = z),
+    cbind(stat = NA, n = 2L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = z, s = z, scale = TRUE),
+    cbind(stat = NA, n = 2L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = z, s = z, adjust = TRUE),
+    cbind(stat = NA, n = 2L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = z, s = z, adjust = TRUE, scale = TRUE),
+    cbind(stat = NA, n = 2L)
+  )
+})
+
+test_that("heuristic_in_bin() returns NA for single obs", {
+  expect_equal(
+    heuristic_in_bin(color = 2, s = 2),
+    cbind(stat = NA, n = 1L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = 2, s = 2, scale = TRUE),
+    cbind(stat = NA, n = 1L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = 2, s = 2, adjust = TRUE),
+    cbind(stat = NA, n = 1L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = 2, s = 2, adjust = TRUE, scale = TRUE),
+    cbind(stat = NA, n = 1L)
+  )
+})
+
+test_that("heuristic_in_bin() returns NA for single obs", {
+  cc <- factor(LETTERS[1:3])
+  expect_equal(
+    heuristic_in_bin(color = cc, s = 1:3),
+    cbind(stat = 1, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = cc, s = 2*(1:3), scale = TRUE),
+    cbind(stat = 4, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = cc, s = 1:3, adjust = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
+  expect_equal(
+    heuristic_in_bin(color = cc, s = 2*(1:3), adjust = TRUE, scale = TRUE),
+    cbind(stat = NA, n = 3L)
+  )
 })
 
 test_that("heuristic() returns average R-squared", {