Reorder factor levels by sorting along another variable

fct_reorder() is useful for 1d displays where the factor is mapped to position; fct_reorder2() for 2d displays where the factor is mapped to a non-position aesthetic. last2() and first2() are helpers for fct_reorder2(); last2() finds the last value of y when sorted by x; first2() finds the first value.

fct_reorder(.f, .x, .fun = median, ..., .desc = FALSE)

fct_reorder2(.f, .x, .y, .fun = last2, ..., .desc = TRUE)

last2(.x, .y)

first2(.x, .y)

Arguments

.f	A factor (or character vector).
.x, .y	The levels of f are reordered so that the values of .fun(.x) (for fct_reorder()) and fun(.x, .y) (for fct_reorder2()) are in ascending order.
.fun	n summary function. It should take one vector for fct_reorder, and two vectors for fct_reorder2, and return a single value.
...	Other arguments passed on to .fun. A common argument is na.rm = TRUE.
.desc	Order in descending order? Note the default is different between fct_reorder and fct_reorder2, in order to match the default ordering of factors in the legend.

Examples

df <- tibble::tribble(
  ~color,     ~a, ~b,
  "blue",      1,  2,
  "green",     6,  2,
  "purple",    3,  3,
  "red",       2,  3,
  "yellow",    5,  1
)
df$color <- factor(df$color)
fct_reorder(df$color, df$a, min)
#> [1] blue   green  purple red    yellow
#> Levels: blue red purple yellow green
fct_reorder2(df$color, df$a, df$b)
#> [1] blue   green  purple red    yellow
#> Levels: purple red blue green yellow

boxplot(Sepal.Width ~ Species, data = iris)
boxplot(Sepal.Width ~ fct_reorder(Species, Sepal.Width), data = iris)
boxplot(Sepal.Width ~ fct_reorder(Species, Sepal.Width, .desc = TRUE), data = iris)

chks <- subset(ChickWeight, as.integer(Chick) < 10)
chks <- transform(chks, Chick = fct_shuffle(Chick))

if (require("ggplot2")) {
ggplot(chks, aes(Time, weight, colour = Chick)) +
  geom_point() +
  geom_line()

# Note that lines match order in legend
ggplot(chks, aes(Time, weight, colour = fct_reorder2(Chick, Time, weight))) +
  geom_point() +
  geom_line() +
  labs(colour = "Chick")
}
#> Loading required package: ggplot2