Overlay two scatter charts into one (with ggplot)

Question

I have 2 data frames for males and another for females (the variables are the same, crc and maxilla). From each of these df generated two charts. Now I’m trying to combine them into just one chart, but as they have number of different lines I can’t do.

The df are as follows::

alometria_M_max = (data.frame(crc_M, maxilla_M))

      crc_M maxilla_M
1  5.897154  1.398717
2  6.102559  1.560248
3  6.173786  1.640937
4  6.001415  1.515127
5  5.926926  1.388791
6  5.926926  1.458615
7  5.863631  1.558145
8  5.960232  1.528228
9  5.880533  1.437463
10 6.082219  1.547563
11 5.973810  1.521699
12 5.918894  1.458615
13 5.855072  1.423108
14 5.808142  1.283708

alometria_F_max = (data.frame(crc_F, maxilla_F))

      crc_F maxilla_F
1  6.198479  1.576915
2  6.295266  1.701105
3  6.418365  1.884035
4  6.393591  1.818077
5  6.120297  1.665818
6  6.142037  1.633154
7  6.139885  1.615420
8  5.855072  1.543298
9  5.913503  1.665818
10 6.165418  1.479329
11 6.107023  1.607436
12 6.214608  1.710188
13 6.171701  1.684545

Graphics

plot_M <- ggplot(alometria_M_max, aes(x=crc_M, y= maxilla_M)) + 
  geom_point(color="green") + 
  theme_bw() + 
  theme_classic() + 
  geom_smooth(method = "lm", se= FALSE, color= "green")

plot_F <- ggplot(alometria_F_max, aes(x=crc_F, y= maxilla_F)) + 
  geom_point(color="red") + 
  theme_bw() + 
  theme_classic() + 
  geom_smooth(method = "lm", se= FALSE, color= "red")

Will someone please have an idea of how to put these two graphs together in just one, with the regression slope lines visible?

Answer 1

Like almost everything in ggplot2, the best way to solve graphics display problems is by organizing the data frame. In case, I suggest it be a data frame only, with three columns: crc, maxilla and grupo. The group column shall indicate which crc and maxilla belongs to each group, in case M or F.

Below I show how was my solution:

crc_M <- c(5.897154, 6.102559, 6.173786, 6.001415, 
  5.926926, 5.926926, 5.863631, 5.960232, 
  5.880533, 6.082219, 5.973810, 5.918894, 
  5.855072, 5.808142)

maxilla_M <- c(1.398717, 1.560248, 1.640937, 1.515127, 
  1.388791, 1.458615, 1.558145, 1.528228, 
  1.437463, 1.547563, 1.521699, 1.458615, 
  1.423108, 1.283708)

crc_F <- c(6.198479, 6.295266, 6.418365, 6.393591,
           6.120297, 6.142037, 6.139885, 5.855072, 
           5.913503, 6.165418, 6.107023, 6.214608, 
           6.171701)

maxilla_F <- c(1.576915, 1.701105, 1.884035, 1.818077, 
               1.665818, 1.633154, 1.615420, 1.543298, 
               1.665818, 1.479329, 1.607436, 1.710188, 
               1.684545)

alometria <- data.frame(crc = c(crc_M, crc_F),
                        maxilla = c(maxilla_M, maxilla_F),
                        grupo = rep(c("M", "F"), 
                                    c(length(crc_M), length(crc_F))))

library(ggplot2)

ggplot(alometria, aes(x = crc, y = maxilla, colour = grupo, group = grupo)) +
  geom_point() +
  geom_smooth(aes(colour = grupo), method = "lm", se = FALSE)
#> `geom_smooth()` using formula 'y ~ x'

^{Created on 2020-11-04 by the reprex package (v0.3.0)}