为什么在此脚本中进行绘图时ggplot2会忽略因子水平顺序？

Question

据我所知，通过控制相关因子水平的顺序，可以最好地控制图例中项目的顺序。但是，当我设置因子水平的顺序时，生成的图似乎忽略了它们（请参见下面的代码）。从其他问题看来，子集数据框可能是造成此问题的原因。我正在从包含大量不同类型特征的大表开始，绘制蛋白质序列示意图上特征位置的图表。这意味着我无法避免对数据进行子集设置，以允许我以不同的方式绘制不同的特征。

所以我的问题是：

1）在这种情况下，如何控制图例中项目的顺序？2）理想情况下，我希望每个geom_point图层都有一个单独的图例-因此，我有一个名为“ Motifs”的主题，另一个为“ PTM”。这可能吗？

library(tidyverse)

df <- as.data.frame(
  type = as.factor(c("Chain", "PTM", "PTM", "Motif", "Motif", "PTM", "Motif", "Chain", "PTM", "PTM", "Motif", "Motif")),
  description = as.factor(c("seq", "methyl", "methyl", "RXL", "RXL", "amine", "CXXC", "seq", "amine", "methyl", "CXXC", "RXL")),
  begin = c(1, 20, 75, 150, 67, 289, 100, 1, 124, 89, 73, 6),
  order = c(1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2),
  length = c(300, 1, 1, 1, 1, 1, 1, 350, 1, 1, 1, 1)
)

plot_start <- -100
plot_end <- 500

dfplot <- ggplot() +
  xlim(plot_start, plot_end) +
  scale_y_continuous(expand = c(0,0), limits =c(0, 2.5))

# white background
dfplot <- dfplot + theme_bw() +  
  theme(panel.grid.minor=element_blank(),
        panel.grid.major=element_blank()) +
  theme(axis.ticks = element_blank(),
        axis.text.y = element_blank()) +
  theme(panel.border = element_blank())

#plot chains
dfplot <- dfplot + geom_rect(data= df[df$type == "Chain",],
                                               mapping=aes(xmin=begin,
                                                           xmax=length,
                                                           ymin=order-0.2,
                                                           ymax=order+0.2),
                                               colour = "blue",
                                               fill = "#C4D9E9")

#set desired order of factor levels
df$description<-factor(df$description, levels = c("amine", "methyl", "RXL", "seq", "CXXC"))

#plot motif positions

dfplot <- dfplot + geom_point(data = filter(df, type == "Motif"),
                                       aes(begin, order, shape = description, color = description), 
                                       size = 3,)

#plot modification positions

dfplot <- dfplot + geom_point(data = filter(df, type == "PTM"),
                              aes(begin, (order + 0.25), shape = description, color = description), 
                              size = 3) 

dfplot

Answer 1

建议与您的图表略有不同：

suppressPackageStartupMessages( library(dplyr) )
suppressPackageStartupMessages( library(ggplot2) )

df <- data.frame(
        type = as.factor(c("Chain", "PTM", "PTM", "Motif", "Motif", "PTM", "Motif", "Chain", "PTM", "PTM", "Motif", "Motif")),
        description = as.factor(c("seq", "methyl", "methyl", "RXL", "RXL", "amine", "CXXC", "seq", "amine", "methyl", "CXXC", "RXL")),
        begin = c(1, 20, 75, 150, 67, 289, 100, 1, 124, 89, 73, 6),
        order = c(1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2),
        length = c(300, 1, 1, 1, 1, 1, 1, 350, 1, 1, 1, 1)
)

df %>% 
        ggplot(. , aes(x = begin, y = type, colour = description) ) +
        geom_point()