how to make a graph with two lines and four symbols?

Question

I want to make a graph with two lines (one for a level and anorther for other level of the factor), but each level have two categories on ggplot2. So I need make a graph like this (image) but with two symbols for each line. Help, please!!!!

Answer 1

A (potential) solution in R base is this:

Define your data in a dataframe:

df <- data.frame(Gender = c(rep("m",10), rep("f", 10)),
       Age = sample(10:90, 20, replace = T),
       Fitness_level = sample(1:10, 20, replace = T))

Add two distinct point characters depending on age level:

df$pch <- ifelse(df$Age > 40, 8, 12) # 8 and 12 are point characters

Plot fitness level against age for men and, respectively for women, adding for each a regression line:

# scatter plot:
plot(df$Fitness_level[df$Gender=="m"] ~ df$Age[df$Gender=="m"], pch = df$pch,     col="red", ylim=c(1,10))

# regression line for men:
abline(lm(df$Fitness_level[df$Gender=="m"] ~ df$Age[df$Gender=="m"]), col="red")

# add points for women:
points(df$Fitness_level[df$Gender=="f"] ~ df$Age[df$Gender=="f"], pch = df$pch, col = "blue")

# add regression line:
abline(lm(df$Fitness_level[df$Gender=="f"] ~ df$Age[df$Gender=="f"]), col="blue")