How to get coordinates from a R plotly figure - r

Question

I have been struggling like mad to solve an apparently basic question.
Imagine you have a scatter plot, with say ... 10 markers.
I suppose this plot has been generated using plotly within a Shiny environment.
One can easily get the coordinates of these markers using the event_data("plotly_click") code.
Now imagine you do not need the coordinates of these markers, but the coordinates generated by a mouse click but precisely where no marker exists (for example because you would like to set a new marker exactly there, and you would like to re-use the information coming from that mouse click).
I cannot obtain such a behavior using onclick(), or whatever.
Any idea ?

Answer 1

You could add a D3 event listener to your plot
Plotly.d3.select('.plotly').on('click', function(d, i) {})
and then
retrieve the relative x and y values based on the click position (d3.event.layerX resp. layerY)
adjusting for the relative graph position (document.getElementsByClassName('bg')[0].attributes['x'])
and finally calculating the new values based on the axis ranges (myPlot.layout.xaxis.range[0])
The new x and y value are then pushed to the existing graph
Plotly.extendTraces(myPlot, {
x: [[x]],
y: [[y]]
}, [1]);
Complete R code
library("plotly")
library("htmlwidgets")
p <- plot_ly(x = c( -2, 0, 2 ),y = c( -2, 1, 2), type = 'scatter' ,mode = 'lines+markers') %>%
add_trace(x=c(-1,0.4,2),y=c(2, 0, -1),type='scatter',mode='lines+markers') %>%
layout(hovermode='closest')
javascript <- "
var myPlot = document.getElementsByClassName('plotly')[0];
Number.prototype.between = function (min, max) {
return this >= min && this <= max;
};
Plotly.d3.select('.plotly').on('click', function(d, i) {
var e = Plotly.d3.event;
var bg = document.getElementsByClassName('bg')[0];
var x = ((e.layerX - bg.attributes['x'].value + 4) / (bg.attributes['width'].value)) * (myPlot.layout.xaxis.range[1] - myPlot.layout.xaxis.range[0]) + myPlot.layout.xaxis.range[0];
var y =((e.layerY - bg.attributes['y'].value + 4) / (bg.attributes['height'].value)) * (myPlot.layout.yaxis.range[0] - myPlot.layout.yaxis.range[1]) + myPlot.layout.yaxis.range[1]
if (x.between(myPlot.layout.xaxis.range[0], myPlot.layout.xaxis.range[1]) &&
y.between(myPlot.layout.yaxis.range[0], myPlot.layout.yaxis.range[1])) {
Plotly.extendTraces(myPlot, {
x: [[x]],
y: [[y]]
}, [1]);
}
});"
p <- htmlwidgets::prependContent(p, onStaticRenderComplete(javascript), data=list(''))
p
Interactive Javascript example
var traces = [{
x: [1, 2, 3, 4],
y: [10, 15, 13, 17],
mode: 'markers',
type: 'scatter'
}];
traces.push({
x: [2, 3, 4, 5],
y: [16, 5, 11, 9],
mode: 'markers',
type: 'scatter'
});
traces.push({
x: [1, 2, 3, 4],
y: [12, 9, 15, 12],
mode: 'markers',
type: 'scatter'
});
traces.push({
x: [],
y: [],
mode: 'lines+markers',
type: 'scatter'
});
var myPlot = document.getElementById('myPlot')
Plotly.newPlot('myPlot', traces, {hovermode: 'closest'});
Number.prototype.between = function(min, max) {
return this >= min && this <= max;
};
Plotly.d3.select(".plotly").on('click', function(d, i) {
var e = Plotly.d3.event;
var bg = document.getElementsByClassName('bg')[0];
var x = ((e.layerX - bg.attributes['x'].value + 4) / (bg.attributes['width'].value)) * (myPlot.layout.xaxis.range[1] - myPlot.layout.xaxis.range[0]) + myPlot.layout.xaxis.range[0];
var y = ((e.layerY - bg.attributes['y'].value + 4) / (bg.attributes['height'].value)) * (myPlot.layout.yaxis.range[0] - myPlot.layout.yaxis.range[1]) + myPlot.layout.yaxis.range[1]
if (x.between(myPlot.layout.xaxis.range[0], myPlot.layout.xaxis.range[1]) &&
y.between(myPlot.layout.yaxis.range[0], myPlot.layout.yaxis.range[1])) {
Plotly.extendTraces(myPlot, {
x: [
[x]
],
y: [
[y]
]
}, [3]);
}
});
<script src="https://cdn.plot.ly/plotly-latest.min.js"></script>
<div id="myPlot" style="width:100%;height:100%"></div>
Shiny example
library(shiny)
library("plotly")
library("htmlwidgets")
ui <- fluidPage(
plotlyOutput("plot")
)
server <- function(input, output) {
javascript <- "
function(el, x){
Number.prototype.between = function (min, max) {
return this >= min && this <= max;
};
Plotly.d3.select('.plotly').on('click', function(d, i) {
var e = Plotly.d3.event;
var bg = document.getElementsByClassName('bg')[0];
var x = ((e.layerX - bg.attributes['x'].value + 4) / (bg.attributes['width'].value)) * (el.layout.xaxis.range[1] - el.layout.xaxis.range[0]) + el.layout.xaxis.range[0];
var y =((e.layerY - bg.attributes['y'].value + 4) / (bg.attributes['height'].value)) * (el.layout.yaxis.range[0] - el.layout.yaxis.range[1]) + el.layout.yaxis.range[1]
if (x.between(el.layout.xaxis.range[0], el.layout.xaxis.range[1]) && y.between(el.layout.yaxis.range[0], el.layout.yaxis.range[1])) {
Plotly.extendTraces(el, {
x: [[x]],
y: [[y]]
}, [1]);
}
});
}"
output$plot <- renderPlotly({
plot_ly(x = c( -2, 0, 2 ),y = c( -2, 1, 2), type = 'scatter' ,mode = 'lines+markers') %>%
add_trace(x=c(-1,0.4,2),y=c(2, 0, -1),type='scatter',mode='lines+markers') %>%
layout(hovermode='closest') %>% onRender(javascript)
})
}
shinyApp(ui = ui, server = server)

Answer 2

The solution by Maximilian does not work on Plotly.js versions later than 1.42.0. Trying to fetch
var bg = document.getElementsByClassName('bg')[0];
returns undefined. The solution works using version 1.41.3.
This answer is most likely more suited to be a comment but my reputation does not meet the minimum requirement of 50.