Bar charts

The Bar graph can be used as follows:

var Bar = require('paths/bar');
var bar = Bar({
  data: [
    [
      { name: 'Italy', population: 59859996 },
      { name: 'Spain', population: 46704314 },
      { name: 'France', population: 65806000 },
      { name: 'Romania', population: 20121641 },
      { name: 'Greece', population: 10815197 }
    ],
    [
      { name: 'Zambia', population: 14580290 },
      { name: 'Cameroon', population: 20386799 },
      { name: 'Nigeria', population: 173615000 },
      { name: 'Ethiopia', population: 86613986 },
      { name: 'Ghana', population: 24658823 }
    ]
  ],
  accessor: function(x) { return x.population; },
  compute: {
    color: function(i) { return somePalette[i]; }
  },
  width: 500,
  height: 400,
  gutter: 10,
  offset: [20, 30],
  max: 200000000,
  min: 0
});

Parameters:

• width, height: have the obvious geometric meaning
• data: contains an array of arrays with the data to plot. The precise form of the data is not important, because the actual value of the data will be extracted by the accessor function. Each array will be represented by a series of bars with the same index.
• accessor: a function that is applied to each datum inside each item in data to extract a numeric value
• offset (optional, default = [0, 0]): how much to shift the bar chart
• gutter (optional, default = 10): the space to leave between each group of bars
• min, max (optional): computed based on the data if missing
• compute (optional): see the introduction.

The bar chart allows multiple histograms to be drawn side by side. If you just have one series to be plotted, put it inside an array of length one anyway, like this:

Bar({
  data: [[2, 5, 3, 9, 7]],
  ...
});

The object returned by the Bar function contains the curves array, on which one can iterate to draw the rectangles. Each member of this array has the properties line, index and item, the latter containing the actual datum associated to the rectangle. It also contain the scale property, containing the scale used on the vertical axis