Geom_line lines order

I'm trying to represent a soil profile where my x axis it's copies g and y is depth 0, 15, 30. But the command geom_line doesn't draw the lines in the correct order:

Frist I've selected the data just from the group Core: 1

subset_data <- subset(data, Core == "1", select = c(Depth, "16S_B", "16S_A"))

And afterwards I draw the plot:

ggplot(subset_data, aes(y = Depth)) +
  geom_line(aes(x = "16S_B", color = "16S_B")) +
  geom_line(aes(x = "16S_A", color = "16S_A")) +
  labs(x = "Value", y = "Depth", color = "Variable") +
  scale_color_manual(values = c("16S_B" = "blue", "16S_A" = "red")) +
  ggtitle("Gráfico de líneas de 16S_B y 16S_A para Core 1") +
  scale_y_reverse(limits = c(31, 4)) +
  scale_x_log10()

But I get this:

And I need the lines to be ordered like this:

ggplot(subset_data, aes(x = Depth)) +
  geom_line(aes(y = "16S_B", color = "16S_B")) +
  geom_line(aes(y = "16S_A", color = "16S_A")) +
  labs(y = "Value", x = "Depth", color = "Variable") +
  scale_color_manual(values = c("16S_B" = "blue", "16S_A" = "red")) +
  ggtitle("Gráfico de líneas de 16S_B y 16S_A para Core 1") +
  scale_x_reverse(limits = c(31, 4)) +
  scale_y_log10()

How do I tell geom_line to link my dots in 0-15-30 order?

By default (see ?geom_line)

> geom_line() connects in order of the variable on the x axis.

To connect the points in the order of the variable on the y axis you could set orientation = "y".

Using some fake example data:

subset_data <- data.frame(
  check.names = FALSE,
  Depth = c(1, 15, 30),
  "16S_B" = c(3, 1, 2),
  "16S_A" = c(1, 3, 2)
)

library(ggplot2)

ggplot(subset_data, aes(y = Depth)) +
  geom_line(aes(x = `16S_B`, color = "16S_B"), orientation = "y") +
  geom_line(aes(x = `16S_A`, color = "16S_A"), orientation = "y") +
  labs(x = "Value", y = "Depth", color = "Variable") +
  scale_color_manual(values = c("16S_B" = "blue", "16S_A" = "red")) +
  ggtitle("Gráfico de líneas de 16S_B y 16S_A para Core 1") +
  scale_y_reverse()

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Or as a second option switch the role of x and y and use coord_flip():

ggplot(subset_data, aes(x = Depth)) +
  geom_line(aes(y = `16S_B`, color = "16S_B")) +
  geom_line(aes(y = `16S_A`, color = "16S_A")) +
  labs(x = "Value", y = "Depth", color = "Variable") +
  scale_color_manual(values = c("16S_B" = "blue", "16S_A" = "red")) +
  ggtitle("Gráfico de líneas de 16S_B y 16S_A para Core 1") +
  scale_x_reverse() +
  coord_flip()

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