[data analysis and visualization] key points of data drawing 10- construction of legend

Key points of data drawing 10- Construction of legend

Legend is a key part of data visualization to convey information , So it's important to create the right legend . This article describes how to set up ggplot2 Title in legend 、 Text 、 Location 、 Symbols etc. .

ggplot2 Legend settings

ggplot2 Create default legend

By default , As long as the shape feature is mapped to ggplot Called aes() Variables in the section ,ggplot2 The legend will be automatically generated on the chart . therefore , If you are in ggplot2 Set colors in 、 Shape or transparency , The legend will be created by default . If you want to see ggplot2 Information that can be set , call ggplot2::theme that will do .

#  load ggplot2
library(ggplot2)
#  Show your own mtcars data 
head(mtcars)

A data.frame: 6 × 11

	mpg	cyl	disp	hp	drat	wt	qsec	vs	am	gear	carb
	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>	<dbl>
Mazda RX4	21.0	6	160	110	3.90	2.620	16.46	0	1	4	4
Mazda RX4 Wag	21.0	6	160	110	3.90	2.875	17.02	0	1	4	4
Datsun 710	22.8	4	108	93	3.85	2.320	18.61	1	1	4	1
Hornet 4 Drive	21.4	6	258	110	3.08	3.215	19.44	1	0	3	1
Hornet Sportabout	18.7	8	360	175	3.15	3.440	17.02	0	0	3	2
Valiant	18.1	6	225	105	2.76	3.460	20.22	1	0	3	1

#  mapping 
#  The horizontal axis wt, The vertical axis mpg, Color cyl, shape factor
basic <- ggplot(mtcars, aes(wt, mpg, colour = factor(cyl), shape = factor(vs) )) +
       geom_point()
basic

Change legend title labs()

labs() The function allows you to change the legend title . You can specify a title for each part of the legend , That is, every aesthetics used in the chart aesthetics .

#  Set the legend title based on the default chart 
basic+
  labs(
         colour = "colour",
         shape = "shape"
        )

Deletion of legend information

adopt theme() and guides() You can delete the entire legend or a specific part of the legend .

#  Delete shape
basic + guides(shape=FALSE) +
labs(
     colour = "colour",
     shape = "shape"
    )

Warning message:
"`guides(<scale> = FALSE)` is deprecated. Please use `guides(<scale> = "none")` instead."

#  Delete legend 
basic + theme(legend.position = "none")

Control legend position

ggplot2 Allow legend to be placed anywhere . If you put the legend around the chart , Use legend.position Options and specify top,right,bottom, or left. To place the legend in the drawing area , Specify a length of 2 Vector , Both values are in 0 and 1 Between , And give x and y Coordinates are OK .

#  Place the legend on the left side of the chart 
basic + theme(legend.position = "left")

#  Place the legend on the left side of the chart 
# legend.justification After setting the legend position , The specific location of the legend 
basic + theme(legend.position = "left",legend.justification = c("left", "center"))

basic + theme(
    legend.position = c(0.55, 0.95), #  Set the starting position of the legend , The bottom left corner is the origin , The range of abscissa and ordinate is 0 To 1
    legend.justification = c("right", "top"), # After setting the legend position , The specific location of the legend 
    legend.box.just = "right", #  Set different legend alignment 
    legend.margin = margin(6, 6, 6, 6) #  Set the outer margin of the legend content 
    )

Legend appearance settings

Here are 4 Example , Shows how to customize the main functions of the legend ：

• legend.box Custom legend outline
• legend.key Set each variable in the legend key Value presentation information
• legend.text Set legend font
• legend.title Set legend title

#  Custom legend outline 
basic + theme(
    #  Set the outline color 
    legend.box.background = element_rect(color="red", size=2),
    #  Set the outline margin 
    legend.box.margin = margin(36, 6, 6, 6)
)

#  Set each variable in the legend key Value presentation information 
basic + theme(legend.key = element_rect(fill = "blue", colour = "black"))

#  Custom legend font color 
basic + theme(legend.text = element_text(size = 8, colour = "red"))

#  Set legend title 
basic + theme(legend.title = element_text(face = "bold",colour = 'red'))

Reference resources

• Building a nice legend with R and ggplot2