提供给连续比例的离散值

Question

知道为什么scale_x_continuous(limits=c(-10, 10))会抛出此错误？

Error: Discrete value supplied to continuous scale

代码：

> head(sign.m)
             miRNA variable  value
1   hsa-miR-99a-5p      100  -1.37
2 hsa-miR-92a-1-5p      100   3.11
3     hsa-miR-9-5p      100  -3.60
4   hsa-miR-877-5p      100   2.08
5     hsa-miR-7-5p      100   3.37
6  hsa-miR-642a-5p      100  -5.10

ggplot(sign.m, aes(miRNA,as.numeric(value))) + geom_boxplot() +
  theme_bw(base_size = 8) + 
  theme(axis.text.x = element_text( angle = 90)) +
  coord_flip() +
  labs(x = "miRNA", y = "log2 tumor/benign") +
  scale_x_continuous(limits=c(-10, 10))

> summary(sign.m)
             miRNA         variable       value          
 hsa-miR-129-5p :  48   100    :  50   Length:2400       
 hsa-miR-3152-5p:  48   106    :  50   Class :character  
 hsa-miR-135a-5p:  48   122    :  50   Mode  :character  
 hsa-miR-204-5p :  48   124    :  50                     
 hsa-miR-1224-5p:  48   126    :  50                     
 hsa-miR-139-5p :  48   134    :  50                     
 (Other)        :2112   (Other):2100