15 Questions All R Users Have About Plots                                                                                                        Posted                                                         on July 30th, 2015
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http://blog.datacamp.com/15-questions-about-r-plots/

1. How To Draw An Empty R Plot?画一个空的图

2. How To Set The Axis Labels And Title Of The R Plots?设置坐标和标题
3. How To Add And Change The Spacing Of The Tick Marks Of Your R Plot更改坐标轴的标度
4. How To Create Two Different X- or Y-axes2套坐标轴（主要是Y)
5. How To Add Or Change The R Plot’s Legend?添加、改变小标签
6. How To Draw A Grid In Your R Plot?背景图上画网格
7. How To Draw A Plot With A PNG As Background?用PNG做背景图
8. How To Adjust The Size Of Points In An R Plot?局部缩放
9. How To Fit A Smooth Curve To Your R Data添加光滑曲线

10. How To Add Error Bars In An R Plot添加错误柱形图
11. How To Save A Plot As An Image On Disc保存图片到硬盘
12. How To Plot Two R Plots Next To Each Other?多图输出（并列等）
13. How To Plot Multiple Lines Or Points?多曲线输出
14. How To Fix The Aspect Ratio For Your R Plots显示缩放
15. What Is The Function Of hjust And vjust In ggplot2?不懂，乱入。。。。。。。。