Add a horizontal discrete legend below the chart in ggvis

Question

I'd like to make a horizontal legend below the ggvis chart. I can use legend properties to place it below the chart, but don't know how to make the labels horizontal below the legend title. Below is the minimum reproducible code (grabbed from the web).

df1 = data.frame(x=sample(1:10), y=sample(1:10))
df2 = data.frame(x=1:10, y=1:10)
df3 = data.frame(x=1:10, y=sqrt(1:10))

df2$id <- 1
df3$id <- 2
df4    <- rbind(df2,df3)
df4$id <- factor(df4$id)

df4 %>% ggvis(x=~x, y=~y, stroke=~id) %>% layer_lines() %>%
    # make sure you use add relative scales
    add_relative_scales() %>%
    # values for x and y need to be between 0 and 1
    # e.g for the x-axis 0 is the at far-most left point and 1 at the far-right 
    add_legend("stroke", title="Cylinders",
               properties=legend_props(
                   legend=list(
                       x=scaled_value("x_rel", 0.2),
                       y=scaled_value("y_rel", -.2)
                   ))) %>%
    layer_points(x=~x, y=~y, data=df1, stroke:='black') 

Palinode

Since this still seems to be an open issue over at the ggvis GitHub developer page, I doubt this is possible without a major hack. But I could be wrong. – Carolincarolina

@Carolincarolina Any idea if this feature has been added to ggvis yet? – Franctireur

Does my answer seem like what you are looking for? – Franctireur

Answer 1

This is most certainly a hack, but works great:

df4 %>% ggvis(x=~x,y=~y,stroke=~id) %>% layer_lines() %>%
  #make sure you use add relative scales
  add_relative_scales() %>%
  #values for x and y need to be between 0 and 1
  #e.g for the x-axis 0 is the at far-most left point and 1 at the far-right 
  add_legend("stroke", title = "Cylinders", values = c(1, 1),
             properties = legend_props(
               legend = list(
                 x = scaled_value("x_rel", 0.2),
                 y = scaled_value("y_rel", -.2)
               ))) %>%
  add_legend("stroke", title = " ", values = c(2, 2),
             properties = legend_props(
               legend = list(
                 x = scaled_value("x_rel", 0.23),
                 y = scaled_value("y_rel", -.2)
               ))) %>%
  layer_points(x=~x,y=~y,data = df1,stroke:='black') 

Basically, I'm adding another add_legend, setting the title as blank, adjusting the scale_value so that it is very close to the first legend but not overlapping. I then set the first legend with values = c(1,1) and the second with values = c(2,2) so that the two values stack on top of each other. This makes it look like one legend with horizontal values.

Franctireur

Answer 2

Seen that ggvis is dormant now, maybe you may consider switching to googleVis.

Here's a similar plot you can get by manipulating a little bit your sample data:

df5 <- df4[df4$id==1,]
colnames(df5)[2] <- "y1"

library(tidyverse)

df5 <- df5 %>%
  mutate(
    y0 = df1[order(df1$x),c(2)],
    y2 = sqrt(x)
  )

df5 <- df5[, c(1,4,2,5)]

library(googleVis)

plot_df5 <- gvisLineChart(df5, options=list(
                                            legend="bottom",
                                            series =
                                            "[{labelInLegend: 'Dot', color: 'black'},                                            
                                            {labelInLegend: 'Cylinders: 1', color: 'blue', curveType: 'dot'},
                                            {labelInLegend: 'Cylinders: 2', color: 'orange'}]"
                                           )
                         )
plot(plot_df5)

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