d3、複数のパスを更新

var d0 = [{
    id: "A",
    values: [{
      x: .25,
      y: .9
    }, {
      x: .75,
      y: 1
    }]
  },
  {
    id: "B",
    values: [{
      x: .25,
      y: .5
    }, {
      x: .8,
      y: .4
    }]
  },
  {
    id: "C",
    values: [{
      x: .1,
      y: .1
    }, {
      x: .9,
      y: .1
    }]
  }
]


var d1 = [{
    id: "A",
    values: [{
      x: 0,
      y: 1
    }, {
      x: 1,
      y: 1
    }]
  },
  {
    id: "B",
    values: [{
      x: 0,
      y: .5
    }, {
      x: 1,
      y: .5
    }]
  },
  {
    id: "C",
    values: [{
      x: 0,
      y: 0
    }, {
      x: 1,
      y: 0
    }]
  }
]

var svg = d3.select("svg")

var margin = {
  top: 20,
  right: 80,
  bottom: 30,
  left: 50
}
var width = svg.attr("width") - margin.left - margin.right
var height = svg.attr("height") - margin.top - margin.bottom

g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")")

var scaleX = d3.scaleLinear().range([0, width]).domain([0, 1])
var scaleY = d3.scaleLinear().range([height, 0]).domain([0, 1])

g.append("g")
  .attr("class", "axis axis--x")
  .attr("transform", "translate(0," + height + ")")
  .call(d3.axisBottom(scaleX));

g.append("g")
  .attr("class", "axis axis--y")
  .call(d3.axisLeft(scaleY))

var line = d3.line()
  .x(function(d) {
    return scaleX(d.x)
  })
  .y(function(d) {
    return scaleY(d.y)
  });

var lineg = g.selectAll(".lineg")
  .data(d0)
  .enter()
  .append("g")
  .attr("class", "lineg");

lineg.append("path")
  .attr("class", "line")
  .attr("d", function(d) {
    return line(d.values)
  })

function update() {
  var i = g.selectAll(".lineg")
    .data(d1)

  i.enter()
    .append("g")
    .attr("class", "lineg")

  i.exit()
    .remove()

  i.select(".line")
    .datum(function(d) {
      return d;
    })
    .attr("d", function(d) {
      return line(d.values)
    })
}

.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 1.5px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/6.2.0/d3.min.js"></script>
<svg width="500" height="300"></svg>
<br/>
<button onclick="update()">Change</button>