ggplot2's line legends appear "crossed-out" - r

Question

I'm creating a ggplot with two lines, each from separate geoms. As an example:
df = data.frame(
x.v = seq(0, 1, 0.025),
y.v = runif(41)
)
straight.line = data.frame(
Inter = c(0),
Slope = c(1)
)
p = ggplot() +
geom_point(
mapping = aes(
x = x.v,
y = y.v
),
data = df,
colour = "blue"
) +
geom_smooth(
mapping = aes(
x = x.v,
y = y.v,
colour = "line of best fit"
),
data = df,
method = "lm",
show.legend = NA
) +
geom_abline(
mapping = aes(
intercept = Inter,
slope = Slope,
colour = "y = x"
),
data = straight.line,
show.legend = NA
) +
guides(
fill = "none",
linetype = "none",
shape = "none",
size = "none"
)
This gives the output:
As you can see, the legend has weird diagonal lines through it. An answer to a similar question says this can be fixed by using show.legend = NA. However, as you can see in the code above, I did this and it did not change the result.
Does anybody know what is adding the diagonal lines in the legend and how else I can fix it please? Thanks.
EDIT: A question of if this is a duplicate of this. This may be the answer but how do I apply this when the answer in the link uses fill, and I use colour, please?
If I try
+ guides(colour = guide_legend(override.aes = list(colour = NULL)))
I get the error
Error in check.length("col") : 'gpar' element 'col' must not be length 0
and if I try
+ guides(colour = guide_legend(override.aes = listfill = NULL)))
I get the error
Error in `$<-.data.frame`(`*tmp*`, "fill", value = character(0)) :
replacement has 0 rows, data has 1

Answer 1

The following works:
library(ggplot2)
ggplot() +
geom_point(mapping = aes(x = x.v, y = y.v),
data = df, colour = "blue") +
geom_smooth(mapping = aes(x = x.v, y = y.v, colour = "line of best fit"),
data = df, method = "lm", show.legend = NA) +
geom_abline(mapping = aes(intercept = Inter, slope = Slope, colour = "y = x"),
data = straight.line, show.legend = FALSE) +
guides(fill = "none", linetype = "none", shape = "none", size = "none")
The code can be made a little bit less repetitive and we can leave out some things (liek the guide-call):
ggplot(data = df, mapping = aes(x = x.v, y = y.v)) +
geom_point(colour = "blue") +
geom_smooth(aes(colour = "line of best fit"), method = "lm") +
geom_abline(mapping = aes(intercept = Inter, slope = Slope, colour = "y = x"),
data = straight.line, show.legend = FALSE)
Why do we need to use show.legend = FALSE here and not show.legend = NA?
From the documentation:
show.legend
logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display
This means that is we use show.legend = NA for the geom_abline-call we use this layer in the legend. However, we don't want to use this layer and therefore need show.legend = FALSE. You can see that this does not influence, which colors are included in the legend, only the layer.
Data
set.seed(42) # For reproducibilty
df = data.frame(x.v = seq(0, 1, 0.025),
y.v = runif(41))
straight.line = data.frame(Inter = 0, Slope = 1)