Add regression line and equation just in the first line of a facet_grid

[Gabbi]

Hello everyone,

I am trying to add a regression line in a facet grid graphs, but only in the first line.
When I use the function geom_smooth() all graphs appear with the regression line.
I tryied to insert a "if" funtion, but gets me an error message.

Here is my code:
p <- ggplot(datar, aes(x = Ano, y = area_taxa,group = usos)) +
geom_line(aes(color = usos), size = 1) +
geom_smooth(method="lm", size = 0.8, lty = "dashed", color = "red") +
theme(legend.position = "none") +
theme(axis.text.y = element_text(size = 18, color = "black"),
axis.text.x = element_text(size=15, color = "black"),
axis.title.x = element_text(size = 20),
axis.title.y = element_text(size = 20),
legend.text = element_text(size=20),
strip.text.x = element_text(size = 18),
strip.text.y = element_text(size = 18)) +
labs(x = "Year", y = "") + ggtitle("") +
facet_grid(tipo_f~usos_f, scales = "free_y")+
scale_x_continuous(breaks = seq(1985,2020,10))

I tryied the add:
if(tipo_f = "(A) Land use (Mha)"){
geom_smooth(method="lm", size = 0.8, lty = "dashed", color = "red")}

I also need the equations to be shown in the graphs.

Can someone help me please?!

[Leon]

Try modifying your data prior to plotting, like so:

# Load libraries ----------------------------------------------------------
library("tidyverse")


# Create example data -----------------------------------------------------
n <- 100
set.seed(232153)
my_data <- tibble(
  x1 = rnorm(n),
  x2 = rnorm(n),
  g1 = sample(LETTERS[1:3], size = n, replace = TRUE),
  g2 = sample(LETTERS[4:6], size = n, replace = TRUE),
)


# Augment data ------------------------------------------------------------
my_data <- my_data %>% 
  mutate(x1_A_D = case_when(g1 == "A" & g2 == "D" ~ x1,
                            TRUE ~ NA_real_),
         x2_A_D = case_when(!is.na(x1_A_D) ~ x2,
                            TRUE ~ NA_real_))


# Visualise ---------------------------------------------------------------
my_data %>% 
  ggplot(aes(x = x1, y = x2)) + 
  geom_line() +
  geom_smooth(aes(x = x1_A_D, y = x2_A_D),
              method = "lm", linetype = "dashed") +
  theme_minimal() +
  facet_grid(vars(g2), vars(g1))

Yielding:

[Gabbi]

Uaaau...it worked ver well!! Thank you!!
Can you also help me in showing the equations in the graphs, please?

[Leon]

Google is your friend: https://www.statology.org/add-regression-equation-to-plot-in-r/

[Gabbi]

Thanks!! It worked too!! But now I am trying to break Y axis, to gave a better resolution, I am trying to find in google but still nothing, can you help me again, please?
I'd like to break just the second line of graphs.

[Gabbi]

[Leon]

You had this in your initial example, look at your "scales" in your facets

[Gabbi]

Actually the initial example was incomplete, this one is the final plot. The broken axis is something I can try latter. Thank you very much for your help!!