使用ggplot2更改單個圖形的刻度標記的位置

Question

任何人都知道如何使用ggplot2在R中的單個繪圖的頂部繪製X軸刻度標記？我一直在看教程和郵件列表和Rhelp沒有成功。

在此先感謝。 阿古斯

Answer 1

使用position = 'top'

library(ggplot2) 

# Generate some data 
df = data.frame(x = 1:10, y = 1:10) 

# x-axis breaks 
breaks = 1:10 

# base plot 
p <- ggplot(df, aes(x,y)) + geom_point() + 
    scale_x_continuous(breaks = breaks, position = 'top') + 
    scale_y_continuous(limits = c(0, 11), expand = c(0,0)) + 
    theme_bw() 

使用gtable（有一些更新至2.1.0 ggplot）原液可用。見here

library(ggplot2) 
library(gtable) 
library(grid) 

# Generate some data 
df = data.frame(x = 1:10, y = 1:10) 

# x-axis breaks 
breaks = 1:10 

# base plot 
p <- ggplot(df, aes(x,y)) + geom_point() + 
    scale_x_continuous(breaks = breaks) + 
    scale_y_continuous(limits = c(0, 11), expand = c(0,0)) + 
    theme_bw() 


# Get ggplot grob 
g1 <- ggplotGrob(p) 

## Get the position of the plot panel in g1 
pp <- c(subset(g1$layout, name == "panel", se = t:r)) 

# Title grobs have margins. 
# The margins need to be swapped. 
# Function to swap margins - 
# taken from the cowplot package: 
# https://github.com/wilkelab/cowplot/blob/master/R/switch_axis.R 
vinvert_title_grob <- function(grob) { 
    heights <- grob$heights 
    grob$heights[1] <- heights[3] 
    grob$heights[3] <- heights[1] 
    grob$vp[[1]]$layout$heights[1] <- heights[3] 
    grob$vp[[1]]$layout$heights[3] <- heights[1] 

    grob$children[[1]]$hjust <- 1 - grob$children[[1]]$hjust 
    grob$children[[1]]$vjust <- 1 - grob$children[[1]]$vjust 
    grob$children[[1]]$y <- unit(1, "npc") - grob$children[[1]]$y 
    grob 
} 

# Get xlab and swap margins 
index <- which(g1$layout$name == "xlab-b") 
xlab <- g1$grobs[[index]] 
xlab <- vinvert_title_grob(xlab) 

# Put xlab at the top of g1 
g1 <- gtable_add_rows(g1, g1$heights[g1$layout[index, ]$t], pp$t-1) 
g1 <- gtable_add_grob(g1, xlab, pp$t, pp$l, pp$t, pp$r, clip = "off", name="topxlab") 

# Get x axis (axis line, tick marks and tick mark labels) 
index <- which(g1$layout$name == "axis-b") 
xaxis <- g1$grobs[[index]] 

# Swap axis ticks and tick mark labels 
ticks <- xaxis$children[[2]] 
ticks$heights <- rev(ticks$heights) 
ticks$grobs <- rev(ticks$grobs) 

# Move tick marks 
    # Get tick mark length 
    plot_theme <- function(p) { 
    plyr::defaults(p$theme, theme_get()) 
    } 
    tml <- plot_theme(p)$axis.ticks.length # Tick mark length 

ticks$grobs[[2]]$y <- ticks$grobs[[2]]$y - unit(1, "npc") + tml 

# Swap tick mark labels' margins and justifications 
ticks$grobs[[1]] <- vinvert_title_grob(ticks$grobs[[1]]) 

# Put ticks and tick mark labels back into xaxis 
xaxis$children[[2]] <- ticks 

# Add axis to top of g1 
g1 <- gtable_add_rows(g1, g1$heights[g1$layout[index, ]$t], pp$t) 
g1 <- gtable_add_grob(g1, xaxis, pp$t+1, pp$l, pp$t+1, pp$r, clip = "off", name = "axis-t") 

# Remove original x axis and xlab 
g1 = g1[-c(9,10), ] 

# Draw it 
grid.newpage() 
grid.draw(g1)