A legend for Sankey networks

[wlandau]

Any plans for sankeyNetwork(NodeGroup = "column_with_color", legend = TRUE)?

[cjyetman]

I don't believe anyone is working on that, but suppose we'd be open to PRs for it.

[fbiga]

Hello, I faced the same issue. Here's the way to add a legend.

You first need to create a d3.js code and store in the working directory. This d3.js code will create a legend, I started from the description in https://www.d3-graph-gallery.com/graph/custom_legend.html (section: categorical legend, use a loop).
I adapted to let it use data for the sankey as input

the d3.js could be called in R using r2d3::r2d3() function.

Then you need the function manipulateWidget::combineWidgets() to pair the sankey from sankeyNetwork and the legend.

I hope this could be useful for implementing a legend = T argument within the sankeyNetwork function.

Here's an example:
the d3.js code
`// create a list of keys
var keys = data

// Usually you have a color scale in your chart already
var color = d3.scaleOrdinal()
.domain(keys)
.range(d3.schemeCategory10)

// Add one dot in the legend for each name.
svg.selectAll("mydots")
.data(keys)
.enter()
.append("circle")
.attr("cx", 50)
.attr("cy", function(d,i){ return 100 + i*25}) // 100 is where the first dot appears. 25 is the distance between dots
.attr("r", 7)
.style("fill", function(d){ return color(d)})

// Add one dot in the legend for each name.
svg.selectAll("mylabels")
.data(keys)
.enter()
.append("text")
.attr("x", 70)
.attr("y", function(d,i){ return 100 + i*25}) // 100 is where the first dot appears. 25 is the distance between dots
// .style("fill", function(d){ return color(d)})
.text(function(d){ return d})
.attr("text-anchor", "left")
.style("alignment-baseline", "middle")`

and here's the R code:
library(networkD3)
library(dplyr)
library(manipulateWidget)
library(r2d3)

links <- data.frame(
source=c("group_A","group_A", "group_B", "group_C", "group_C", "group_E"),
target=c("group_C","group_D", "group_E", "group_F", "group_G", "group_H"),
value=c(2, 3, 2, 3, 1, 3)
) # Make a connection data frame

nodes <- data.frame(
name=c(as.character(links$source), as.character(links$target)) %>%
unique()
) # Make a nodes data frame

links$IDsource <- match(links$source, nodes$name)-1
links$IDtarget <- match(links$target, nodes$name)-1

links$group <- as.factor(c("type_a","type_a","type_a","type_b","type_b","type_b")) # Add a 'group' column to each connection:
nodes$group <- as.factor(c("my_first_group","my_first_group","my_first_group","my_first_group","my_first_group","my_second_group","my_first_group","my_second_group"))

my_color <- 'd3.scaleOrdinal() .domain(["type_a", "type_b", "my_first_group", "my_second_group"]) .range(d3.schemeCategory10)'

sankey <- sankeyNetwork(Links = links, Nodes = nodes, Source = "IDsource", Target = "IDtarget",
Value = "value", NodeID = "name", colourScale=my_color, LinkGroup="group", NodeGroup="group")

legend <- r2d3(data = unique(c(links$group, nodes$group)), script = "legend_test.js") # legend

combineWidgets(sankey, legend, ncol = 2, colsize = c(5,1)) # Combine plots