How to plot a line graph using data from two different dataframes

April 4, 2023

I have these two dataframes:

decils_general:

structure(list(grup_CNAE_Red = c("Total", "Total", "Total", "Total", 
"Total", "Total", "Total", "Total", "Total", "Total"), variable = structure(1:10, levels = c("decil1_inflacio", 
"decil2_inflacio", "decil3_inflacio", "decil4_inflacio", "decil5_inflacio", 
"decil6_inflacio", "decil7_inflacio", "decil8_inflacio", "decil9_inflacio", 
"decil10_inflacio"), class = "factor"), value = c(9.3, 8.9, 8.6, 
8.4, 8.4, 8.4, 8.2, 8.1, 8.2, 7.8)), row.names = c(NA, -10L), class = "data.frame")

and decils_primera:

structure(list(grup_despesa_DGAPE = c("Total", "Total", "Total", 
"Total", "Total", "Total", "Total", "Total", "Total", "Total"
), variable = structure(1:10, levels = c("decil1_inflacio", "decil2_inflacio", 
"decil3_inflacio", "decil4_inflacio", "decil5_inflacio", "decil6_inflacio", 
"decil7_inflacio", "decil8_inflacio", "decil9_inflacio", "decil10_inflacio"
), class = "factor"), value = c(5.8, 5.7, 5.6, 5.3, 5, 4.9, 4.8, 
4.4, 4.4, 3.9)), row.names = c(NA, -10L), class = "data.frame")

I’m trying to plot a graph similar to this one:

So that variable should be the x axis and value the y axis.

I have tried the following, but I’m getting nowhere.

plot_decils_general_primera <- ggplot() +
  geom_line(data = decils_general, aes(x=variable, y=value)) +
  geom_line(data = decils_primera, aes(x=variable, y=value))

>Solution :

The issue is that the variable mapped on x is a discrete variable in which case you have to explicitly set the group aes and you should get a note about that:

geom_line(): Each group consists of only one observation.
ℹ Do you need to adjust the group aesthetic?

To fix that add e.g. group=1 to each of your geom_line which tells ggplot2 to treat all observations as one group which for simplicity we call 1.

library(ggplot2)
library(dplyr)

ggplot() +
  geom_line(data = decils_general, aes(x = variable, y = value, group = 1)) +
  geom_line(data = decils_primera, aes(x = variable, y = value, group = 1))

However, overall I would suggest to bind your datasets into one which in general simplifies the plotting code as you don’t need duplicated layers:

decils <- list(general = decils_general, primera = decils_primera) |>
  dplyr::bind_rows(.id = "dataset")

ggplot(decils, aes(x = variable, y = value, color = dataset, group = dataset)) +
  geom_line() +
  geom_point(aes(fill = dataset), shape = 21, alpha = .5, size = 3) +
  geom_label(aes(label = value, vjust = ifelse(dataset == "general", 0, 1)),
    fill = NA, label.size = 0, label.padding = unit(10, "pt"),
    show.legend = FALSE
  )