如何在ggplot2折线图中设置离散X轴且保留折线

你遇到的折线消失问题，本质是将genes_included转为因子后，ggplot无法自动识别正确的分组来连接折线。以下两种方法都能实现需求：

方法一：保留因子型X轴，显式指定分组 #

转换x轴为因子后，在aes中添加group = interaction(variation, purity)，强制ggplot按variation和purity的组合分组绘制折线：

# 转换x轴为因子
corrtable <- data.frame(
  genes_included = factor(c(rep(100,4),rep(1000,4),rep(5000,4),rep(10000,4))),
  percent_map_to_origin = runif(16),
  variation = rep(c("TCGA", "TCGA", "GTEx", "GTEx"),4),
  purity = rep(c("Included", "Excluded"),8)
)

library(ggplot2)
ggplot(corrtable, aes(x = genes_included, y = percent_map_to_origin, 
                      color = variation, linetype = purity,
                      group = interaction(variation, purity))) +
  geom_line() +
  geom_point() +
  geom_hline(yintercept=0.99554361, color="darkslategray") +
  labs(x = "Number of Genes Included", 
       y = "% of Cell Lines That Correlate Highest to Origin Tissue") +
  theme(text = element_text(face = "bold"), 
        legend.text = element_text(size = 16), 
        legend.title = element_text(size = 18), 
        axis.title = element_text(size = 12), 
        axis.text = element_text(size = 13)) +
  scale_linetype_manual(values=c("dashed", "solid"))

方法二：保留连续X轴，自定义刻度实现离散显示 #

如果不想修改原始数据类型，直接通过scale_x_continuous设置刻度断点和标签，同样能达到仅显示指定X轴值的效果：

# 保留原始数据（x为数值型）
corrtable <- data.frame(
  genes_included = c(rep(100,4),rep(1000,4),rep(5000,4),rep(10000,4)),
  percent_map_to_origin = runif(16),
  variation = rep(c("TCGA", "TCGA", "GTEx", "GTEx"),4),
  purity = rep(c("Included", "Excluded"),8)
)

library(ggplot2)
ggplot(corrtable, aes(x = genes_included, y = percent_map_to_origin, 
                      color = variation, linetype = purity)) +
  geom_line() +
  geom_point() +
  geom_hline(yintercept=0.99554361, color="darkslategray") +
  labs(x = "Number of Genes Included", 
       y = "% of Cell Lines That Correlate Highest to Origin Tissue") +
  theme(text = element_text(face = "bold"), 
        legend.text = element_text(size = 16), 
        legend.title = element_text(size = 18), 
        axis.title = element_text(size = 12), 
        axis.text = element_text(size = 13)) +
  scale_linetype_manual(values=c("dashed", "solid")) +
  scale_x_continuous(breaks = c(100, 1000, 5000, 10000),  # 指定显示的刻度
                     labels = c("100", "1000", "5000", "10000"))  # 刻度标签

两种方法都能实现需求：方法一真正将X轴转为离散型，方法二更适合需要保留数值型X轴属性的场景。

内容的提问来源于stack exchange，提问作者avery