Error: Discrete value supplied to Continuous Scale (error function to position "n" in graph)

Question

I’m crowding a few boxplots to compare, year by year, the grades of students periodized and not periodized. I am using the function below to plot these graphs. Within the function stat_summary I’m using the function give.n that returns the size of each group, filling this "n" in the y = 102 coordinate of the chart.

# Função give.n para calcular o tamanho do grupo:
give.n <- function(x){
  return(c(y = 102, label = length(x)))
}

# boxplot ggplot2:
notas_dp <- ggplot(data = dados3,
               aes(x = dados3$PERIOD, y = dados3$NOTA_FINAL))
notas_dp + geom_boxplot() + 
  facet_grid(. ~ dados3$ANO_DISCIPLINA) +
  labs(x = "\nPeriodização\n",
       y = "\nNotas finais\n",
       title = "Notas finais quanto à periodização dos estudantes aprovados",
       subtitle = "P = periodizado; NP = Não periodizado") +
  scale_y_continuous(name = "Notas finais", breaks = seq(0, 100, 10)) +
  geom_hline(aes(yintercept=70), colour="blue", linetype = "solid") +
  geom_hline(aes(yintercept=50), colour="red", linetype = "solid") +
  stat_summary(fun.data = give.n, geom = "text", fun.y = median)

• My chart is coming out like this:

I tried to change the function give.n so that it returns in the gàafico the information n = 50, for example, and not only the number 50.

# Alteração da função give.n:
give.n <- function(x){
  return(c(y = 102, label = paste("n = ", length(x))))
}

However, when I run my chart it returns the following error:

Erro: Discrete value supplied to continuous scale

I’m having trouble positioning the function paste() of the R base nowhere to concatenate the "n = " together with the function result give.n.

Below follows the output of dput(head(dados3, 10)) (I removed the data from the GRR column as it is not public data, but it is 11 character string).

structure(list(
    GRR = structure(c(23L, 49L, 54L, 56L, 61L, 47L, 
107L, 93L, 60L, 95L), .Label = c("GRR2015****", ..., "GRR2018****"), class = "factor"), 
    ANO_GRR = structure(c(7L, 9L, 9L, 9L, 9L, 9L, 9L, 9L, 9L, 
    9L), .Label = c("2006", "2007", "2008", "2009", "2010", "2011", 
    "2012", "2013", "2014", "2015", "2016", "2017", "2018"), class = "factor"), 
    NOTA_FINAL = c(86, 76, 88, 88, 90, 88, 88, 74, 78, 75), SITU_FINAL = structure(c(1L, 
    1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("Aprovado", 
    "Cancelado", "Reprovado por Frequência", "Reprovado por nota", 
    "Trancamento Total"), class = "factor"), 
    ANO_DISCIPLINA = structure(c(1L, 
    1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("2015", "2016", 
    "2017", "2018"), class = "factor"), 
    PERIOD = structure(c(3L, 
    2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L), .Label = c("Jubilados", 
    "P", "NP"), class = "factor"), 
    PROF = structure(c(3L, 3L, 
    3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("XXXXX", "XXXXX", 
    "XXXXX"), class = "factor"), 
    ANO_DESPERIOD = c(2, 0, 0, 0, 
    0, 0, 0, 0, 0, 0)), 
   .Names = c("GRR", "ANO_GRR", "NOTA_FINAL", 
"SITU_FINAL", "ANO_DISCIPLINA", "PERIOD", "PROF", "ANO_DESPERIOD"
), row.names = c(1L, 3L, 4L, 6L, 7L, 8L, 9L, 10L, 11L, 12L), 
    class = "data.frame")

Thank you if anyone can help. Thank you!

Answer 1

I don’t know if it is possible to do this with stat_summary. One option is to use geom_text:

ggplot(data = dados3,
       aes(x = PERIOD, y = NOTA_FINAL)) +
geom_boxplot() + 
  facet_grid(. ~ ANO_DISCIPLINA) +
  labs(x = "\nPeriodização\n",
       y = "\nNotas finais\n",
       title = "Notas finais quanto à periodização dos estudantes aprovados",
       subtitle = "P = periodizado; NP = Não periodizado") +
  scale_y_continuous(name = "Notas finais", breaks = seq(0, 100, 10)) +
  geom_hline(aes(yintercept=70), colour="blue", linetype = "solid") +
  geom_hline(aes(yintercept=50), colour="red", linetype = "solid") +
  geom_text(inherit.aes = FALSE, data = dados3 %>% group_by(PERIOD) %>% count(), 
             aes(label = paste0("n = ", n), x = PERIOD, y = 102))