Chapter 6 Theme：Axis

theme() layer controls several parts of a graph:

  • axis (座標軸)

  • legend (圖例)

  • panel (圖面)

  • 其他整體外觀的元素：

    • line: 線的設計（使用element_line()）

    • rect: 方塊區的設計（element_rect()）

    • text: 文字（element_text()）

    • 等等。

Here we focus on axis design.

6.1 Elements of axis

axis.xxx, where xxx includes

  • line（座標線）

    types: axis.line / axis.line.x / axis.line.y

    through: element_line()

  • text（刻度文字，即標示點的文字）

    types: axis.text / axis.text.x / axis.text.y

    through: element_text()

  • tick（標示點）

    types: axis.tick / axis.tick.x / axis.tick.y

    through: element_line()

  • title（座標名稱）

    types: axis.title / axis.title.x / axis.title.y

    through: element_text()

6.2 Setup

library(ggplot2)
library(dplyr)
library(showtext)
font_add("QYuan","cwTeXQYuan-Medium.ttf") # 新增字體
showtext_auto(enable=TRUE)
theme_set(theme_classic())
p1 <- ggplot(mtcars, aes(wt, mpg)) +
  geom_point() 
p1

6.3 axis.line

6.3.1 element_line()

Usage: Theme elements

element_line(colour = NULL, size = NULL, linetype = NULL,
  lineend = NULL, color = NULL, arrow = NULL, inherit.blank = FALSE)

6.3.2 Panel grid lines （圖面格線）

p1+
  theme(panel.grid.major.y=element_line())->p1
p1

圖面格線一般會淺色，請修改它。

Y軸的10標線跟X軸線太近，你會如何改？

6.3.3 範例

p1 + theme(axis.line = element_line(size = 3, colour = "grey80"))

《經濟學人》常會把一軸的軸線拿掉，請完成它。

還有一個空白元素：element_blank()

6.4 axis.text

6.4.1 element_text()

Usage: Theme elements

element_text(family = NULL, face = NULL, colour = NULL, size = NULL, hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL, color = NULL, margin = NULL, debug = NULL, inherit.blank = FALSE)

  • face: 粗體，斜體之類設定

  • hjust: 0-1； 0 left-justified (標記在文字左邊)； 1 right-justified (標記在文字右邊)：

  • vjust: 0-1; 0 bottom-justified (標記在文字下方)； 1 top-justified (標記在文字上方)

vjust hjust

vjust hjust

  • lineheight: 行高

6.4.2 範例

p1 + theme(axis.text = element_text(colour = "blue"), axis.text.x = element_text(hjust=1))

mtcars2 <- mtcars[1:15, ]
mtcars2$name <- row.names(mtcars2)

ggplot(mtcars2, aes(x = name, y = mpg, fill = name)) + 
  geom_bar(stat = 'identity', position = "identity") +
  guides(fill = FALSE) + 
  theme(axis.text.x = element_text(angle = 90, vjust=0.5, hjust=0))

6.5 axis.tick

6.5.1 element_line()

6.5.2 範例

p1 + theme(axis.ticks = element_line(size = 2))

p1 + theme(axis.ticks.length = unit(.25, "cm"))

6.6 axis.title

6.6.1 element_text()

6.6.2 範例

p1 + theme(axis.title.y = element_text(size = rel(1.5), angle = 90))

6.7 練習

參考經濟學人的設計，修改上次的CPI趨勢圖。

改變Y軸位置可以用 scale_y_continuous(position = "right")

library(readr)
dataCPI2 <- read_csv("https://raw.githubusercontent.com/tpemartin/github-data/master/dataCPI2.csv")
dataCPI2 %>% ggplot()+
  geom_line(aes(x=年月,y=CPI)) -> basePlot2

breakDates <- c("2003-01-01",
                "2005-01-01",
                "2010-01-01",
                "2015-01-01",
                "2018-01-01")
breakDates %>% ymd() -> breakDates

breakLabels <- c("2003",
                 "2005","2010","2015",
                 "2018")

basePlot2 +
  scale_x_date(limits=c(ymd("2003-01-01"),NA),
               breaks = breakDates,
               labels = breakLabels)