poly(<factor>, ..) should error (unless it is.ordered(.))

git-svn-id: https://svn.r-project.org/R/trunk@88970 00db46b3-68df-0310-9c12-caf00c1e9a41

Author: maechler

doc/NEWS.Rd

@@ -336,6 +336,10 @@
 
       \item Default column labels are now correctly aligned when printing a
       matrix with right alignment (\PR{18943}, thanks to \I{Mikael Jagan}).
+
+      \item \code{poly(fct, n)} signals an error again, for a
+      non-\code{ordered} factor \code{fct}, thanks to \I{Roland Fuss}'
+      notice on R-devel.
     }
   }
 }

src/library/stats/R/contr.poly.R

@@ -1,7 +1,7 @@
 #  File src/library/stats/R/contr.poly.R
 #  Part of the R package, https://www.R-project.org
 #
-#  Copyright (C) 1995-2022 The R Core Team
+#  Copyright (C) 1995-2025 The R Core Team
 #
 #  This program is free software; you can redistribute it and/or modify
 #  it under the terms of the GNU General Public License as published by
@@ -79,7 +79,8 @@ poly <- function(x, ..., degree = 1, coefs = NULL, raw = FALSE, simple = FALSE)
     }
     if(degree < 1)
         stop("'degree' must be at least 1")
-    if(is.object(x) && mode(x) == "numeric") x <- as.numeric(x) # for POSIXct, Date,..
+    if(is.object(x) && mode(x) == "numeric" && !(is.factor(x) && !is.ordered(x)))
+        x <- as.numeric(x) # for POSIXct, Date, ordered, but *not* (ordinary) factor
     if(raw) {
         Z <- outer(x, 1L:degree, `^`)
         colnames(Z) <- 1L:degree

src/library/stats/man/poly.Rd

@@ -22,8 +22,9 @@ polym  (\dots, degree = 1, coefs = NULL, raw = FALSE)
   evaluate raw polynomials.
 }
 \arguments{
- \item{x, newdata}{a numeric vector or an object with \code{\link{mode}}
-   \code{"numeric"} (such as a \code{\link{Date}}) at which to evaluate the
+ \item{x, newdata}{a numeric vector or an object such as a
+   \code{\link{Date}} with \code{\link{mode}} \code{"numeric"}, including
+   \code{\link{ordered}} but not plain \code{\link{factor}}s at which to evaluate the
    polynomial. \code{x} can also be a matrix.  Missing values are not
    allowed in \code{x}.}
  \item{degree}{the degree of the polynomial.  Must be less than the

tests/reg-tests-1e.R

@@ -2294,6 +2294,20 @@ stopifnot(all.equal(list(l = -E, u = E, n = 2L), pp, tolerance = 1e-12))
 ## n = 1112538 (Lnx 64b) in R <= 4.5.1  ^^^^^^
 
 
+## poly(<factor>, .)
+hf <- c(-1, 1.2, -1.5, -0.75, -2)
+x <-  c("c", "b", "a",  "b", "a")
+xf <- as.factor(x)
+xo <- as.ordered(x)
+tools::assertError(verbose=TRUE, lm(hf ~ poly(x, 2)))
+tools::assertError(verbose=TRUE, lm(hf ~ poly(xf, 2)))
+coef(om <- lm(hf ~ poly(xo, 2)))
+stopifnot(
+    all.equal(coef(om), tolerance = 5e-5,
+              c("(Intercept)" = -0.81, "poly(xo, 2)1" = 1.01, "poly(xo, 2)2" = -1.7105)))
+## poly(xf, .) gave no error in R 4.1.1--4.5.x
+
+
 
 ## keep at end
 rbind(last =  proc.time() - .pt,