GeezerVison

var graphDiv = document.getElementById('myDiv');
var N = 1000;
var color1 = '#7b3294';
var color1Light = '#c2a5cf';
var colorX = '#ffa7b5';
var colorY = '#fdae61';

function randomArray() {
  var out = new Array(N);
  for(var i = 0; i < N; i++) {
    out[i] = Math.random();
  }
  return out;
}
var x = randomArray();
var y = randomArray();

Plotly.newPlot(graphDiv, [{
  type: 'scatter',
  mode: 'markers',
  x: x,
  y: y,
  xaxis: 'x',
  yaxis: 'y',
  name: 'random data',
  marker: {color: color1, size: 10}
}, {
  type: 'histogram',
  x: x,
  xaxis: 'x2',
  yaxis: 'y2',
  name: 'x coord dist.',
  marker: {color: colorX}
}, {
  type: 'histogram',
  x: y,
  xaxis: 'x3',
  yaxis: 'y3',
  name: 'y coord dist.',
  marker: {color: colorY}
}], {
  title: {
    text: 'Lasso around the scatter points to see sub-distributions'
  },
  dragmode: 'lasso',
  xaxis: {
    zeroline: false,
  },
  yaxis: {
    domain: [0.55, 1],
  },
  xaxis2: {
    domain: [0, 0.45],
    anchor: 'y2',
  },
  yaxis2: {
    domain: [0, 0.45],
    anchor: 'x2'
  },
  xaxis3: {
    domain: [0.55, 1],
    anchor: 'y3'
  },
  yaxis3: {
    domain: [0, 0.45],
    anchor: 'x3'
  }
});

graphDiv.on('plotly_selected', function(eventData) {
  var x = [];
  var y = [];

  var colors = [];
  for(var i = 0; i < N; i++) colors.push(color1Light);

  console.log(eventData.points)

  eventData.points.forEach(function(pt) {
    x.push(pt.x);
    y.push(pt.y);
    colors[pt.pointNumber] = color1;
  });

  Plotly.restyle(graphDiv, {
    x: [x, y],
    xbins: {}
  }, [1, 2]);

  Plotly.restyle(graphDiv, 'marker.color', [colors], [0]);
});