ggplot2—x，y 轴置于图中间

简介

ggplot2 的默认x，y轴置于图片左边缘和下边缘，但有时候需要将原点(0,0)放置于图片正中，便于展示数据的象限信息。
另外，自己设置的x，y轴，由于坐标轴有geom_segment()和geom_text()函数构成，则坐标轴的标签文字可以根据geom_text函数进行个性化设置，可以根据颜色，字体，分组，大小等参数进行映射。

函数主体

函数主体来自center-x-and-y-axis-with-ggplot2，然后经过包装形成了draw_axis_line() 函数。

draw_axis_line <- function(length_x, length_y, 
                           tick_step = NULL, lab_step = NULL){
  axis_x_begin <- -1*length_x
  axis_x_end <- length_x
  
  axis_y_begin  <- -1*length_y
  axis_y_end    <- length_y
  
  if (missing(tick_step))
    tick_step <- 1
  
  if (is.null(lab_step))
    lab_step <- 2
  
# axis ticks data
  
  
  tick_x_frame <- data.frame(ticks = seq(axis_x_begin, axis_x_end, 
                                         by = tick_step))
  
  tick_y_frame <-  data.frame(ticks = seq(axis_y_begin, axis_y_end, 
                           by = tick_step))
  
  # axis labels data
  lab_x_frame <- subset(data.frame(lab = seq(axis_x_begin, axis_x_end, 
                                      by = lab_step), zero = 0), 
                        lab != 0)
  
  lab_y_frame <- subset(data.frame(lab = seq(axis_y_begin, axis_y_end,
                                             by = lab_step),zero = 0), 
                        lab != 0)
  
  # set tick length
  tick_x_length = 15/length(tick_x_frame$ticks)/2
  tick_y_length = 8/length(tick_y_frame$ticks)/2
  
  # set zero point
  
  data <- data.frame(x = 0, y = 0)
  p <- ggplot(data = data) +
    
    # draw axis line
    geom_segment(y = 0, yend = 0, 
                 x = axis_x_begin, 
                 xend = axis_x_end,
                 size = 0.5) + 
    geom_segment(x = 0, xend = 0, 
                 y = axis_y_begin, 
                 yend = axis_y_end,
                 size = 0.5) +
    # x ticks
    geom_segment(data = tick_x_frame, 
                 aes(x = ticks, xend = ticks, 
                     y = 0, yend = 0 + tick_x_length)) +
    # y ticks
    geom_segment(data = tick_y_frame, 
                 aes(x = 0, xend = 0 + tick_y_length, 
                     y = ticks, yend = ticks)) + 
    
    # labels
    geom_text(data=lab_x_frame, aes(x=lab, y=zero, label=lab), vjust = 1.5) +
    geom_text(data=lab_y_frame, aes(x=zero, y=lab, label=lab), hjust= 1.5) +
    theme_void() 
  return(p)
  }

用法

1. 将坐标轴设置到中心。

library(ggplot2)
p <- draw_axis_line(20, 4)
p + geom_point(aes(x =1, y =1))