gplot legend problem with geomcol plot and geompoint + geomline plot

November 27, 2023

I made this plot with ggplot, with a bargraph and two line and points plots.

I can’t figure out why also the two line and points plots in the legend have the square around them as for the barplot.
I’d like to remove it, but I can’t understand how.
I attach the image of the plot to help you to understand it better.

Here the ggplot code that I wrote to have this plot.

ggplot(CO2_F,aes(x=Date,group=1))+
  geom_col(aes(y=Water/1.2,colour = "Water"), size = 1.5, fill = "#33CCFF")+
  scale_y_continuous(sec.axis = sec_axis(trans = ~ .*1.2, name = expression(bold(atop(Water,(mm))))))+
  geom_point(aes(y=CO2_Fert,colour = "CO2_Fert"),size = 2)+
  geom_line(data=CO2[!is.na(CO2$CO2_Fert),],aes(y=CO2_Fert,color="CO2_Fert"), size = 1)+
  geom_errorbar(aes(ymin=CO2_Fert-se_Fert, ymax=CO2_Fert+se_Fert,color="CO2_Fert"), width=1,position=position_dodge(0.1))+
  geom_point(aes(y=CO2_Granular,colour = "CO2_Granular"),size = 2)+
  geom_line(data=CO2[!is.na(CO2$CO2_Granular),],aes(y=CO2_Granular,color="CO2_Granular"), size = 1)+
  geom_errorbar(aes(ymin=CO2_Granular-se_Granular, ymax=CO2_Granular+se_Granular,color="CO2_Granular"), width=1,position=position_dodge(0.05))+
  labs(y = expression(bold(atop(CO["2"],("\u03bc"*mol~m^bold("-2")~s^bold("-1"))))), x = "Datetime")+
  scale_color_manual(name = "", values = c("Water" = "#33CCFF","CO2_Fert" = "#5436D9", "CO2_Granular" = "#FF9900"))+
  ggtitle("Fert Vs Granular") +
  scale_x_date(date_labels="%b %d",date_breaks  ="7 days",date_minor_breaks = "1 day",limits = c(as.Date("2023-06-30"), as.Date("2023-09-22")))+
  theme_classic()+theme(legend.position = "top")+
  theme(axis.title.y.left = element_text(margin = margin(r=10),color="black", size=14),
        axis.title.y.right = element_text(margin = margin(l=10),color="black", size=14),
        plot.title = element_text(color="black", size=14, face="bold",hjust = 0.5),
        axis.text.y = element_text(color="black",size=10),
        axis.title.x = element_text(color="black", size=14,face="bold"),
        axis.text.x = element_text(color="black",size=12),
        legend.text = element_text(color = "black", size = 12),
        legend.background = element_blank(),legend.box = "horizontal")

In which line I’ve introduced this error? What should I have to modify?
Someone can help me?
Thanks.

>Solution :

This is not really an error. But getting the legend right when multiple geom and/or aesthetics are involved is kind of an art. (;

The "shape" or symbol used as the legend key is determined by the key_glyph of a geom. And if you have multiple geom layers (e.g. in your case we have four: col, point, line, errorbar) all the key glyphs get merged. In your case the border surrounding the legend keys stems from the key glyph used by geom_col.

From my experience there is not always a "one size fits all" solution to fix the legend. One option which works in your case is to map on the fill aes in geom_col, get rid of the outline by setting linewidth = 0 and add a scale_fill_manual where I set the fill color to "transparent" for the point/line/errobar `.

Second, to make sure that the color and fill legends get merged use the same name= and set limits= to include all three categories.

Using some fake random data:

library(ggplot2)
set.seed(1)

CO2 <- data.frame(
  Date = 1:20,
  Water = runif(20, 1, 8),
  CO2_Fert = runif(20, 2, 3),
  CO2_Granular = runif(20, 3, 4),
  se_Fert = runif(20),
  se_Granular = runif(20)
)

ggplot(CO2, aes(x = Date, group = 1)) +
  geom_col(aes(y = Water / 1.2, fill = "Water"), linewidth = 0) +
  scale_y_continuous(sec.axis = sec_axis(
    trans = ~ . * 1.2,
    name = expression(bold(atop(Water, (mm))))
  )) +
  geom_point(aes(y = CO2_Fert, colour = "CO2_Fert"), size = 2) +
  geom_line(
    data = CO2[!is.na(CO2$CO2_Fert), ],
    aes(y = CO2_Fert, color = "CO2_Fert"), linewidth = 1
  ) +
  geom_errorbar(
    aes(ymin = CO2_Fert - se_Fert, ymax = CO2_Fert + se_Fert, color = "CO2_Fert"),
    width = 1
  ) +
  geom_point(aes(y = CO2_Granular, colour = "CO2_Granular"), size = 2) +
  geom_line(
    data = CO2[!is.na(CO2$CO2_Granular), ],
    aes(y = CO2_Granular, color = "CO2_Granular"), linewidth = 1
  ) +
  geom_errorbar(
    aes(ymin = CO2_Granular - se_Granular, ymax = CO2_Granular + se_Granular, color = "CO2_Granular"),
    width = 1
  ) +
  labs(y = expression(
    bold(atop(CO["2"], ("\u03bc" * mol ~ m^bold("-2") ~ s^bold("-1"))))
  ), x = "Datetime") +
  scale_color_manual(
    name = NULL,
    values = c("Water" = "#33CCFF", "CO2_Fert" = "#5436D9", "CO2_Granular" = "#FF9900"),
    limits = c("Water", "CO2_Fert", "CO2_Granular")
  ) +
  scale_fill_manual(
    name = NULL,
    values = c("Water" = "#33CCFF", "CO2_Fert" = "transparent", "CO2_Granular" = "transparent"),
    limits = c("Water", "CO2_Fert", "CO2_Granular")
  ) +
  ggtitle("Fert Vs Granular") +
  # scale_x_date(date_labels = "%b %d", date_breaks = "7 days", date_minor_breaks = "1 day", limits = c(as.Date("2023-06-30"), as.Date("2023-09-22"))) +
  theme_classic() +
  theme(legend.position = "top") +
  theme(
    axis.title.y.left = element_text(margin = margin(r = 10), color = "black", size = 14),
    axis.title.y.right = element_text(margin = margin(l = 10), color = "black", size = 14),
    plot.title = element_text(color = "black", size = 14, face = "bold", hjust = 0.5),
    axis.text.y = element_text(color = "black", size = 10),
    axis.title.x = element_text(color = "black", size = 14, face = "bold"),
    axis.text.x = element_text(color = "black", size = 12),
    legend.text = element_text(color = "black", size = 12),
    legend.background = element_blank(), legend.box = "horizontal"
  )