D3-Draw Grid Line At A Location Based On The Y Coordinates?

I am kind a new to d3.js and want to draw a horizontal grid line based on y coordinate value fiddle , i've tried with if condition at y1 and y2 locations but the lines are overlapp

Solution 1:

Your if statement makes little sense to me:

if (y(d) === thresholdValues.minValue) {
    return y(d);
}

This means that only when the value in the screen is exactly thresholdValues.minValue (which is 40 in your code) the line will be painted.

Answer : drop the if statement. Actually, I kept the if just to avoid the first gridline, over the x axis:

if (d != 0) {
    return y(d);
}

Here is your code with that change:

var margin = {
  top: 30,
  right: 20,
  bottom: 30,
  left: 50
};

var thresholdValues = {
  minValue: 40,
  maxValue: 85
};
var width = 600 - margin.left - margin.right;
var height = 270 - margin.top - margin.bottom;

var parseDate = d3.time.format("%d-%b-%y").parse;

var x = d3.time.scale().range([0, width]);
var y = d3.scale.linear().range([height, 0]);

var xAxis = d3.svg.axis().scale(x)
  .orient("bottom").ticks(5);

var yAxis = d3.svg.axis().scale(y)
  .orient("left").ticks(5);

var valueline = d3.svg.line()
  .x(function(d) {
    return x(d.date);
  })
  .y(function(d) {
    return y(d.close);
  });

var svg = d3.select("body")
  .append("svg")
  .attr("width", width + margin.left + margin.right)
  .attr("height", height + margin.top + margin.bottom)
  .append("g")
  .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

// Get the data
var data = [{
  date: "1-May-12",
  close: "58.13"
}, {
  date: "30-Apr-12",
  close: "53.98"
}, {
  date: "27-Apr-12",
  close: "67.00"
}, {
  date: "26-Apr-12",
  close: "89.70"
}, {
  date: "25-Apr-12",
  close: "99.00"
}];

data.forEach(function(d) {
  d.date = parseDate(d.date);
  d.close = +d.close;
});

// Scale the range of the data
x.domain(d3.extent(data, function(d) {
  return d.date;
}));
y.domain([0, 100]);

svg.append("path") // Add the valueline path.
  .attr("d", valueline(data));

svg.append("g") // Add the X Axis
  .attr("class", "x axis")
  .attr("transform", "translate(0," + height + ")")
  .call(xAxis);

svg.append("g") // Add the Y Axis
  .attr("class", "y axis")
  .call(yAxis);

svg.selectAll("line.horizontalGrid").data(y.ticks(4)).enter()
  .append("line")
  .attr({
    "class": "horizontalGrid",
    "x1": margin.right,
    "x2": width - margin.right,
    "y1": function(d) {
      if (d != 0) {
        return y(d);
      }
    },
    "y2": function(d) {
      if (d != 0) {
        return y(d);
      }
    },
    "fill": "none",
    "shape-rendering": "crispEdges",
    "stroke": "grey",
    "stroke-width": "2px",
    "opacity": 0.4,
    "stroke-dasharray": 8
  });

body {
  font: 12px Arial;
}

path {
  stroke: steelblue;
  stroke-width: 2;
  fill: none;
}

.axis path,
.axis line {
  fill: none;
  stroke: grey;
  stroke-width: 1;
  shape-rendering: crispEdges;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

EDIT: If you want to draw only two lines, at the thresholds, you have to pass their values to data, not the scale ticks:

.data(Object.values(thresholdValues))

Here is the demo:

var margin = {
  top: 30,
  right: 20,
  bottom: 30,
  left: 50
};

var thresholdValues = {
  minValue: 40,
  maxValue: 85
};
var width = 600 - margin.left - margin.right;
var height = 270 - margin.top - margin.bottom;

var parseDate = d3.time.format("%d-%b-%y").parse;

var x = d3.time.scale().range([0, width]);
var y = d3.scale.linear().range([height, 0]);

var xAxis = d3.svg.axis().scale(x)
  .orient("bottom").ticks(5);

var yAxis = d3.svg.axis().scale(y)
  .orient("left").ticks(5);

var valueline = d3.svg.line()
  .x(function(d) {
    return x(d.date);
  })
  .y(function(d) {
    return y(d.close);
  });

var svg = d3.select("body")
  .append("svg")
  .attr("width", width + margin.left + margin.right)
  .attr("height", height + margin.top + margin.bottom)
  .append("g")
  .attr("transform", "translate(" + margin.left + "," + margin.top + ")");

// Get the data
var data = [{
  date: "1-May-12",
  close: "58.13"
}, {
  date: "30-Apr-12",
  close: "53.98"
}, {
  date: "27-Apr-12",
  close: "67.00"
}, {
  date: "26-Apr-12",
  close: "89.70"
}, {
  date: "25-Apr-12",
  close: "99.00"
}];

data.forEach(function(d) {
  d.date = parseDate(d.date);
  d.close = +d.close;
});

// Scale the range of the data
x.domain(d3.extent(data, function(d) {
  return d.date;
}));
y.domain([0, 100]);

svg.append("path") // Add the valueline path.
  .attr("d", valueline(data));

svg.append("g") // Add the X Axis
  .attr("class", "x axis")
  .attr("transform", "translate(0," + height + ")")
  .call(xAxis);

svg.append("g") // Add the Y Axis
  .attr("class", "y axis")
  .call(yAxis);

svg.selectAll("line.horizontalGrid").data(Object.values(thresholdValues)).enter()
  .append("line")
  .attr({
    "class": "horizontalGrid",
    "x1": margin.right,
    "x2": width - margin.right,
    "y1": function(d) {
      if (d != 0) {
        return y(d);
      }
    },
    "y2": function(d) {
      if (d != 0) {
        return y(d);
      }
    },
    "fill": "none",
    "shape-rendering": "crispEdges",
    "stroke": "grey",
    "stroke-width": "2px",
    "opacity": 0.4,
    "stroke-dasharray": 8
  });

path {
  stroke: steelblue;
  stroke-width: 2;
  fill: none;
}

.axis path,
.axis line {
  fill: none;
  stroke: grey;
  stroke-width: 1;
  shape-rendering: crispEdges;
}

<script src="https://d3js.org/d3.v3.js"></script>