Why Ggplot2 Legend Not Show in The Graph

Reasons that ggplot2 legend does not appear

You are going about the setting of colour in completely the wrong way. You have set colour to a constant character value in multiple layers, rather than mapping it to the value of a variable in a single layer.

This is largely because your data is not "tidy" (see the following)

head(df)
  x           a          b          c
1 1 -0.71149883  2.0886033  0.3468103
2 2 -0.71122304 -2.0777620 -1.0694651
3 3 -0.27155800  0.7772972  0.6080115
4 4 -0.82038851 -1.9212633 -0.8742432
5 5 -0.71397683  1.5796136 -0.1019847
6 6 -0.02283531 -1.2957267 -0.7817367

Instead, you should reshape your data first:

df <- data.frame(x=1:10, a=rnorm(10), b=rnorm(10), c=rnorm(10))
mdf <- reshape2::melt(df, id.var = "x")

This produces a more suitable format:

head(mdf)
 x variable       value
1 1        a -0.71149883
2 2        a -0.71122304
3 3        a -0.27155800
4 4        a -0.82038851
5 5        a -0.71397683
6 6        a -0.02283531

This will make it much easier to use with ggplot2 in the intended way, where colour is mapped to the value of a variable:

ggplot(mdf, aes(x = x, y = value, colour = variable)) + 
    geom_point() + 
    geom_line()

R: ggplot2 legend not showing up

This is more or less the same as @Allan Cameron already provides.

I want to emphasize the rule of thumb: What is in aes will get a legend.

This helped me a lot to handle legend issues.

And additionally although not recommended here is the solution with the wide format of your data. In some cases it would be necessary to keep the wide format:

ggplot() + 
   geom_line(data = d, aes(x = iteration, y = State_1, color = "blue")) + 
   geom_line(data = d, aes(x = iteration, y = State_2, color = "red")) + 
   geom_line(data = d, aes(x = iteration, y = State_3, color = "green")) + 
   xlab('Number of Iterations') + 
   ylab('Probability of Being in a Certain State') 

Legend does not show up in ggplot2

All you needed to do is move the color param inside the aes

library(ggplot2)

# Sample data using dput
TC_merge <- structure(list(Location = c(0.01, 0.02, 0.03, 0.04), C_r_base = c(59.09, 
  54.18, 54.27, 54.36), C_a_base = c(80.0629, 80.1257, 80.1886, 
    80.2515), C_a_after = c(57.5824, 57.6648, 57.7473, 57.8297)), row.names = c(NA, 
      -4L), class = "data.frame")

# create the manual color scale
manual_color_scale <- c("black", "navyblue", "red4")
names(manual_color_scale) <- c("black", "navyblue", "red4")

ggplot(TC_merge, aes(x=Location)) + 
  # Here I move the color param inside - Though it is a value.
  # The actual color could be random generated.
  # So it is needed to define the color scale
  geom_line(aes(y = C_r_base, color = "black"),  linetype="dashed",
            # I use the size for bigger line to see the color better
            size = 1) + 
  geom_line(aes(y = C_a_base, color = "navyblue"), size = 1) +
  geom_line(aes(y = C_a_after, color = "red4"), size = 1) + theme_classic() + 
  theme(legend.position="right") +
  labs(x = "Distance from CBD (kilometres)",
    y = "Round-trip generalised transport costs (DKK)") + 
  scale_x_continuous(expand = c(0, 0)) +
  scale_y_continuous(expand = c(0, 0)) +
  # Here I defined the manual scale for color
  scale_color_manual(values = manual_color_scale) +
  theme(text=element_text(family="Cambria", size=12))

Here is the plot with legend

^{Created on 2021-03-31 by the reprex package (v1.0.0)}

ggplot2 legend not showing up

Use legend.justification:

library(tidyverse)
ggplot(as.data.frame(cbind(x,y)), aes(x, y)) +
  geom_line() +
  geom_point(aes(2.5,5.5,  colour = "red"), 
             shape = 18, 
             size = 3) +
  ggtitle("Efficient Frontier") +
  xlab("Volatility (Weekly)") +
  ylab("Expected Returns (Weekly)") +
  theme(plot.title = element_text(size=14, face="bold.italic", hjust = 0.5, margin=margin(0,0,15,0)),
        axis.title.x = element_text(size = 10, margin=margin(15,0,0,0)),
        axis.title.y = element_text(size = 10, margin=margin(0,15,0,0)),
        panel.border = element_rect(colour = "black", fill=NA, size=1),
        legend.position = "bottom", 
        legend.justification = "right")

ggplot2 legend is not matching even with manual overrides

I think the use of the list data_plot1 as a list of data frames is not a good choice for plotting purposes. You can split the geoms on several data frames (points, texts, etc) and have a better control of the aes. See an example

colours <- data.frame(
  purple = "#411D64",
  blue = "#486C8B",
  green = "#70B87B"
)

library(ggplot2)
library(latex2exp)

size_y_s0 <- data.frame(
  name = "Size Anchor",
  shape = "size0",
  x = 0,
  y = 1,
  colour = colours$blue
)

size_y_sn <- data.frame(
  name = "Size Response",
  shape = "size*",
  x = 0.4,
  y = 0.9,
  colour = colours$blue
)

income_x_s0 <- data.frame(
  name = "Income Anchor",
  shape = "income0",
  x = 1,
  y = 0,
  colour = colours$green
)

income_x_sn <- data.frame(
  name = "Income Response",
  shape = "income*",
  x = 0.9,
  y = 0.4,
  colour = colours$green
)

size_y_dcc <- data.frame(
  name = "$D^{c}_{c}$",
  x = c(0, 0.4),
  y = c(1, 0.9),
  colour = colours$blue
)
size_y_dcc_text <- data.frame(
  name = "$D^{c}_{c}$",
  text_x = 0.38,
  text_y = 0.99,
  angle = 352
)
size_y_dcp <- data.frame(
  name = "$D^{c'}_{c}$",
  x = c(0, 0.9),
  y = c(1, 0.4),
  colour = colours$green
)

size_y_dcp_text <- data.frame(
  name = "$D^{c'}_{c}$",
  text_x = 0.8,
  text_y = 0.56,
  angle = 340
)

# data frames for the plot
df_points <- rbind(
  size_y_s0,
  size_y_sn,
  income_x_s0,
  income_x_sn
)
df_tex <- rbind(size_y_dcp_text, size_y_dcc_text)

ggplot() +
  # Lines
  geom_line(
    data = size_y_dcc,
    aes(x = x, y = y), colour = size_y_dcc$colour, size = 5, show.legend = FALSE
  ) +
  geom_line(
    data = size_y_dcp,
    aes(x = x, y = y), colour = size_y_dcp$colour, size = 5, show.legend = FALSE
  ) +
  # Points
  geom_point(data = df_points, aes(x, y, shape = shape, fill = shape), size = 5) +
  scale_shape_manual(
    name = "Legend",
    guide = "legend",
    values = c(23, 21, 23, 21), labels = df_points$name
  ) +
  scale_fill_manual(
    values = rev(df_points$colour), labels = df_points$name,
    name = "Legend", guide = "legend"
  ) +
  annotate(
    geom = "text",
    x = df_tex$text_x,
    y = df_tex$text_y,
    label = TeX(df_tex$name),
    size = 10,
    angle = df_tex$angle
  )

---

Related Topics