Interactions (Interactive)

Important

The axis labels will only show in light mode!

viewof slope_a = Inputs.range([-5, 5], {step: 0.01, label: "a slope "});

viewof intercept_a = Inputs.range([-20, 20], {step: 1, label: "a intercept"});

viewof slope_b = Inputs.range([-5, 5], {step: 0.01, label: "b slope "});
viewof intercept_b = Inputs.range([-20, 20], {step: 1, label: "b intercept"});

viewof x_center = Inputs.range([-5, 5], {step: 0.01, label: "x centering"});

maximal = (5 * 5) + 20;


a_at_x = (x_center * slope_a) +intercept_a;
b_at_x = (x_center * slope_b) +intercept_b;
a_at_x1 = ((x_center+1) * slope_a) +intercept_a;
b_at_x1 = ((x_center+1) * slope_b) +intercept_b;



b_eff = b_at_x - a_at_x;
b_counter = b_at_x + slope_a;
interaction =  b_at_x1 - b_counter;

myline = [
  {x: -5, y: (-5 * slope_a)+intercept_a, group: "a"},
  {x: 5, y: (5 * slope_a)+intercept_a, group: "a"},
  {x: -5, y: (-5 * slope_b)+intercept_b, group: "b"},
  {x: 5, y: (5 * slope_b)+intercept_b, group: "b"}
]

interceptPoint = [
  {x: x_center, y: (x_center * slope_a) +intercept_a}
];

arrowLine = [
  {
    from_x: x_center,
    to_x: x_center,
    from_y: (x_center * slope_a) +intercept_a,
    to_y: (x_center * slope_b) +intercept_b
  }
]

a_step = [
  {x: x_center, y: (x_center * slope_a) +intercept_a, group: "a"},
  //{x: x_center, y: (x_center+1 * slope_a) +intercept_a},
  {x: x_center+1, y: ((x_center+1) * slope_a) + intercept_a, group: "a"}
];

b_step = [
  {x: x_center, y: b_at_x, group: "a"},
  //{x: x_center, y: (x_center+1 * slope_a) +intercept_a},
  {x: x_center+1, y: b_at_x + slope_a, group: "a"}
];

b_interaction = [
  {from_x: x_center+1,
   to_x: x_center+1,
   from_y: b_counter,
   to_y: b_at_x1,
   group: "b"
  }
];

Plot.plot({
  y: {domain: [-maximal, maximal]},
  x: {domain: [-5, 6]},
  marks: [
    Plot.lineY(myline, {x: "x", y: "y", stroke: "group", strokeWidth: 4}),
    Plot.arrow(arrowLine,
      {
        x1: "from_x",
        x2: "to_x",
        y1: "from_y",
        y2: "to_y",
        stroke: "red",
        strokeWidth: 3
      }
    ),
    Plot.arrow(b_interaction,
      {
        x1: "from_x",
        x2: "to_x",
        y1: "from_y",
        y2: "to_y",
        stroke: "group",
        strokeWidth: 3
      }
    ),
    Plot.line(a_step,
      {
        x: "x",
        y: "y",
        curve: "step-after",
        stroke: "group",
        strokeDasharray: [2],
        strokeWidth: 2
      }
    ),
    Plot.line(b_step,
      {
        x: "x",
        y: "y",
        curve: "step-after",
        stroke: "group",
        strokeDasharray: [5],
        strokeWidth: 2
      }
    ),
    Plot.dot(interceptPoint, {x: "x", y: "y", fill: "black", r: 5}),
    Plot.text(myline, {
      filter: d => d.x === 5,
      x: 4.8,
      y: "y",
      text: "group",
      fill: "group",
      fontSize: 20
    })
  ]
})

What you’d see in the regression results for lm(y~x*group)

regressionTable = [
  {
    term: "Intercept",
    estimate: a_at_x,
    symbol: "black dot"
  },
  {
    term: "x",
    estimate: slope_a,
    symbol: "dashed blue step"
  },
  {
    term: "groupb",
    estimate: (b_at_x - a_at_x),
    symbol: "red arrow"
  },
  {
    term: "x:groupb",
    estimate: (slope_b - slope_a),
    symbol: "orange arrow"
  }
];
Inputs.table(regressionTable, {sort: false})

Reuse