X轴因子GGTRAP缺失图

以下工作正常:

my_df <- data.frame(x_val = 1:10, y_val = sample(1:20,10), 
            labels = sample(c("a", "b"), 10, replace = T))
ggplot(data = my_df, aes(x = x_val, y = y_val)) + geom_line()

但如果我有机会 x_val

my_df <- data.frame(x_val = 1:10, y_val = sample(1:20,10), 
          labels = sample(c("a", "b"), 10, replace = T))
my_df$x_val <- as.factor(my_df$x_val)
ggplot(data = my_df, aes(x = x_val, y = y_val)) + geom_line()

消息:

geom_path: Each group consists of only one observation. Do you
need to adjust the group aesthetic?

很明显我可以放弃 factor scale_x_discrete(breaks = 1:10,labels= my_df$labels) . 这是我借的地方 link