Don't multiple by 1 or 0 in tree results (#162)

Author: EmilHvitfeldt

NEWS.md

@@ -20,6 +20,8 @@
 
 - linear models such as `lm()` and `glm()` now work with interactions created with `*` and `:`. (#74) 
 
+- Cubist rules will return simplified rules whenever possible to avoid multiplying by 0 and 1. (#152)
+
 # tidypredict 0.5.1
 
 - Exported a number of internal functions to be used in {orbital} package

R/tree.R

@@ -110,12 +110,24 @@ generate_tree_node <- function(node, calc_mode = "") {
       prediction,
       ~ {
         if (.x$is_intercept) {
+          if (.x$val == 0) {
+            return(NULL)
+          }
           return(expr(!!.x$val))
         } else if (.x$op == "multiply") {
+          if (.x$val == 0) {
+            return(NULL)
+          }
+
+          if (.x$val == 1) {
+            return(expr(!!as.name(.x$col)))
+          }
+
           return(expr_multiplication(as.name(.x$col), .x$val))
         }
       }
     )
+    pl <- purrr::discard(pl, is.null)
     pl <- reduce_addition(pl)
   } else {
     if (is.list(prediction) && prediction[[1]]$is_intercept) {

tests/testthat/test-tree.R

@@ -260,6 +260,48 @@ test_that("generate_tree_node() avoids ifelse if path is always TRUE (#143)", {
   )
 })
 
+test_that("generate_tree_node() avoids multipliying with 0 and 1 (#152)", {
+  node <- list(
+    path = list(
+      list(type = "conditional", col = "disp", val = 100, op = "more")
+    ),
+    prediction = list(
+      list(col = "(Intercept)", val = 0, op = "none", is_intercept = 1),
+      list(col = "hp", val = 4, op = "multiply", is_intercept = 0),
+      list(col = "drat", val = 2, op = "multiply", is_intercept = 0)
+    )
+  )
+
+  expect_identical(
+    generate_tree_node(node, calc_mode = "ifelse"),
+    quote(ifelse(disp > 100, hp * 4 + drat * 2, 0))
+  )
+  expect_identical(
+    generate_tree_node(node, calc_mode = ""),
+    quote(disp > 100 ~ hp * 4 + drat * 2)
+  )
+
+  node <- list(
+    path = list(
+      list(type = "conditional", col = "disp", val = 100, op = "more")
+    ),
+    prediction = list(
+      list(col = "(Intercept)", val = 14, op = "none", is_intercept = 1),
+      list(col = "hp", val = 1, op = "multiply", is_intercept = 0),
+      list(col = "drat", val = 0, op = "multiply", is_intercept = 0)
+    )
+  )
+
+  expect_identical(
+    generate_tree_node(node, calc_mode = "ifelse"),
+    quote(ifelse(disp > 100, 14 + hp, 0))
+  )
+  expect_identical(
+    generate_tree_node(node, calc_mode = ""),
+    quote(disp > 100 ~ 14 + hp)
+  )
+})
+
 test_that("path_formulas() works", {
   expect_identical(
     path_formulas(