How to modify only the line of the legend that identifies the group?

Question

How can I change only the thickness of the color lines in the caption that identify the groups?

I do not send the dput() graph pq are more than 40 thousand lines. I send a cutout of the figure to identify my problem and send the graph generation code. I tried a few options on Theme() but I couldn’t change.

require(ggplot2)

pl <- ggplot(TEPT_CONT_TA_TOC, aes(x = time, y = value, colour = grupo,
                 group = interaction(grupo, variable))) +
  geom_line(alpha = 0.5) + geom_smooth(aes(group = grupo), colour = "black") +
  scale_x_continuous(name = "Tempo em segundos",
                     limits = c(0,300),
                     breaks = seq(0,300,by = 60)) +
  scale_y_continuous(name = expression(paste("(",mu,"S)"))) +
  theme(legend.text = element_text(face = "bold",size = 12),
        legend.title = element_text(size = 12),
        legend.key = element_rect(fill = "white"),
        legend.background = element_rect(fill = "white")) +
  labs(title = "Resposta Galvânica da Pele",
       subtitle = "Behavioral Endocrinology Lab",
       colour = "Grupo")

How I make these lines thicker for easier identification of the group?

Answer 1

It was difficult to find a solution. I did it with some cambiarras, but it worked. Basically, I doubled the command geom_line() for an interval beyond the limits of the y-axis: value01+100.

require(ggplot2)
# ANTES
ggplot(economics_long, aes(x=date, y=value01)) +
  geom_line(aes(x=date, y=value01,colour=variable),alpha=0.5)+
  scale_y_continuous(limits=c(0,max(economics_long$value01)))

# DEPOIS
ggplot(economics_long, aes(x=date, y=value01)) +
  geom_line(aes(x=date, y=value01,colour=variable),alpha=0.5,show.legend = F)+
  geom_line(aes(x=date, y=100+value01,colour=variable),alpha=1,size=2,show.legend = T)+
  scale_y_continuous(limits=c(0,max(economics_long$value01)))

# Warning message:
# Removed 2870 rows containing missing values (geom_path).

Answer 2

A solution can be found in Stack Overflow in English.
I’ll still use the chart from reply user’s João Pedro Bazzo Vieira.

Is used guides to give another value to aesthetic size with override.aes, and theme to take the background color from the caption lines.

library(ggplot2)

ggplot(economics_long, aes(x = date, y = value01)) +
  geom_line(aes(colour = variable), alpha = 0.5) +
  guides(colour = guide_legend(override.aes = list(size = 2))) +
  theme(legend.key = element_rect(fill = NA))