使用ggplot2的序数因子的密度直方图

Question

我有一个简单的数据集，如下所示：

ul
  each account in accountlist
    li(class='no-bullets'): form(id='get-account-info'): input(type='hidden', name= account)
    button(class='btn', action='submit')= account

等级是9个等级的序数因子，学校是2个等级的因素。

school       score     grade subject
Your school  83.27     1     English
All schools 113.60     6     English

我想使用密度函数绘制带有ggplot2的刻面直方图。如果我尝试没有密度，我得到这个：

'data.frame':   12762 obs. of  4 variables:
 $ school : Factor w/ 2 levels "Your school",..: 1 2 2 2 2 2 2 2 2 2 ...
 $ score  : num  83.3 113.6 109.2 117.4 100.3 ...
 $ grade  : Ord.factor w/ 9 levels "1"<"2"<"3"<"4"<..: 1 6 6 7 4 3 6 1 6 6 ...
 $ subject: chr  "English" "English" "English" "English" ...

当我添加密度以标准化y轴时，我得到：

p <- ggplot(ss, aes(x=grade))
p <- p + geom_histogram() 
p <- p + facet_wrap(~school)

我错过了什么？

Answer 1

R无法计算因子上的密度，即使是有序因子也是如此。您最好的选择是将grade转换为数字（例如使用as.numeric(as.character(x))）。

xy <- data.frame(school = sample(c("your", "all"), size = 100, replace = TRUE),
                   grade = sample(1:10, size = 100, replace = TRUE))
xy$grade.factor <- factor(xy$grade, ordered = TRUE)

library(ggplot2)

# doesn't work for factors
ggplot(xy, aes(x = grade.factor)) +
  theme_bw() +
  geom_histogram(aes(y = ..density..)) +
  facet_wrap(~ school)

# works for integers/numeric
ggplot(xy, aes(x = grade)) +
  theme_bw() +
  geom_histogram(aes(y = ..density..)) +
  facet_wrap(~ school)