Can't change legend title of ggplot

Can't change this legend title!

I have been trying to change the legend title, but nothing has worked. I've gone through these forums and every thing people have suggested has not worked (guides, manipulating things like scale_color_continuous, etc.).

The other issue is that the "size" function in the geom_point aes command shows in the legend (i.e., it gives a shape to the size command under the shapes for my actual data).

I've been trying for hours to fix these issues, so any help would be appreciated.

Here is the reproducible code to produce the chart:

## Create data frame
Predictor <- c("No", "Yes", "No", "Yes")
TimePoint <- c("Pre", "Pre", "Post", "Post")
value <- c(33, 32, 31, 40)
SE <- c(1.5, 1.5, 1.5, 1.5)
dataframe <- data.frame(Predictor, TimePoint, estimate, SE)

## Define factors and reorder levels of TimePoint
dataframe$TimePoint <- as.factor(dataframe$TimePoint)
dataframe$Predictor <- as.factor(dataframe$Predictor)
dataframe$TimePoint = factor(dataframe$TimePoint, levels = c("Pre", "Post"), ordered = TRUE)

## Create Plot
ggp <- ggplot(data=dataframe, aes(x=TimePoint, y=value, group=Predictor)) +
  geom_errorbar(aes(ymin=value-SE, ymax=value+SE), width=.1) +
  geom_line()+
  geom_point(aes(shape=Predictor, size=2)) +
  coord_cartesian(ylim = c(0, 50)) + ## specifies upper and lower of y
  ylab("Value") +
  xlab("
       Timing")+
  scale_x_discrete(expand = c(0,0.25)) +
  scale_y_continuous(breaks = seq(0, 50, 5), limits = c(0, 50), expand = c(0, 0)) +
  theme_classic() +
  theme(axis.line = element_line(size = .6, colour = "black", linetype=1),         
        axis.text = element_text( angle = 0, color="black", size=18, face=2),
        axis.title.x = element_text(color="black", size=18, face=2),
        axis.title.y = element_text(color="black", size=18, face=2, margin=margin(r=20)))

print(ggp)

I have tried every recommendation I have found on here. Things like the following:

ggp + scale_color_discrete(name = "New Legend Title")

ggp + labs(color = "New Legend Title")

ggp + scale_fill_discrete(name="New Legend Title")

ggp + guides(col = guide_color(title = "New Legend Title"))

ggp + labs(color = "New Legend Title")

Please try the below code,

remove the size from aes() and keep it outside aes() in geom_point
use shape in guides

ggp <- ggplot(data=dataframe, aes(x=TimePoint, y=value, group=Predictor)) +
  geom_errorbar(aes(ymin=value-SE, ymax=value+SE), width=.1) +
  geom_line()+
  geom_point(aes(shape=Predictor), size=4) +
  coord_cartesian(ylim = c(0, 50)) + ## specifies upper and lower of y
  ylab("Value") +
  xlab("
       Timing")+
  scale_x_discrete(expand = c(0,0.25)) +
  scale_y_continuous(breaks = seq(0, 50, 5), limits = c(0, 50), expand = c(0, 0)) +
  theme_classic() +
  theme(axis.line = element_line(size = .6, colour = "black", linetype=1),         
        axis.text = element_text( angle = 0, color="black", size=18, face=2),
        axis.title.x = element_text(color="black", size=18, face=2),
        axis.title.y = element_text(color="black", size=18, face=2, margin=margin(r=20))) +
  guides(shape=guide_legend(title="New Legend Title"))

print(ggp)

Size problem:

Arguments passed to aes() are mappings of your data to the aesthetic elements of the graph. When the aesthetic isn't supposed to be mapped with your data, it is just a constant argument (i.e. size = 2 versus shape = Predictor), you want to pass the argument outside aes():

geom_point(aes(shape=Predictor), size=2)

Legend name problem:

Also, each aesthetic (color, fill, size, alpha, etc.) has it's own legend, and you have to specify which one you're wanting to change. In the examples you gave at the end, you were manipulating the color aes., but you want to manipulate the shape aes.:

• ggp + scale_shape_discrete(name = "New Legend Title")
• ggp + labs(shape = "New Legend Title")
• ggp + guides(col = guide_shape(title = "New Legend Title"))

Extra:

The size argument for width of a line is deprecated, use linewidth instead:

theme(axis.line = element_line(linewidth = .6, colour = "black", linetype=1))