Preserve order of dimnames.

Closes #19

NEWS.md

@@ -1,5 +1,8 @@
 # Version 1.3.0.99
 
+* `melt.array()` creates factor variables with levels in the same order
+  as the original rownames (#19)
+
 * `recast()` now returns a data frame instead of a list (#45).
 
 * `melt.data.frame()` gains a `factorsAsStrings` argument (`TRUE` by default)

R/melt.r

@@ -170,7 +170,14 @@ melt.data.frame <- function(data, id.vars, measure.vars, variable.name = "variab
 #' melt(a)
 melt.array <- function(data, varnames = names(dimnames(data)), ...,
                        na.rm = FALSE, as.is = FALSE, value.name = "value") {
-  var.convert <- function(x) if(is.character(x)) type.convert(x) else x
+  var.convert <- function(x) {
+    if (!is.character(x)) return(x)
+
+    x <- type.convert(x, as.is = TRUE)
+    if (!is.character(x)) return(x)
+
+    factor(x, levels = unique(x))
+  }
 
   dn <- amv_dimnames(data)
   names(dn) <- varnames

inst/tests/test-melt.r

@@ -89,6 +89,18 @@ test_that("dimnames are preserved with arrays and tables", {
   expect_equal(levels(bm$Z), c("A", "B"))
 })
 
+test_that("dimnames kept in original order", {
+  x <- matrix(1:4, nrow = 2)
+  rownames(x) <- c("b", "a")
+  colnames(x) <- c("e", "d")
+  names(dimnames(x)) <- c("x", "y")
+
+  m <- melt(x)
+  expect_equal(levels(m$x), c("b", "a"))
+  expect_equal(levels(m$y), c("e", "d"))
+
+})
+
 test_that("as.is = TRUE suppresses dimnname conversion", {
   x <- matrix(nrow = 2, ncol = 2)
   dimnames(x) <- list(x = 1:2, y = 3:4)