Module: Chartjs::AxisHelpers

Defined in:
lib/chartjs/axis_helpers.rb

Instance Method Summary collapse

Instance Method Details

#calculate_scale_max(value) ⇒ Object

Rounds up value to the next “increment”, where an increment is half the order of magnitude value.

value - a Numeric.

Examples

input  output
  12     15
  15     15
  16     20
1432   1500
7654   8000

Returns an Integer.



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# File 'lib/chartjs/axis_helpers.rb', line 83

def calculate_scale_max(value)
  normalised = normalise value
  quotient, modulus = normalised.divmod 1
  next_increment = if modulus.zero?
                     quotient
                   elsif modulus <= 0.5
                     quotient + 0.5
                   else
                     quotient + 1
                   end
  (next_increment * 10**(order_of_magnitude(value))).to_i
end

#normalise(value) ⇒ Object

Normalises the value to between 0 inclusive and 10.

value - a Numeric.

Returns a Float or 0 if value is nil or zero..



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# File 'lib/chartjs/axis_helpers.rb', line 101

def normalise(value)
  return 0 if value.nil? || value.zero?
  value.to_f / 10**(order_of_magnitude(value))
end

#order_of_magnitude(value) ⇒ Object

Calculates the order of magnitude of value.

value - a Numeric.

Examples

order_of_magnitude(3)
# => 1

order_of_magnitude(13)
# => 1

order_of_magnitude(153)
# => 2

Returns a Integer or 0 if value is nil or zero.



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# File 'lib/chartjs/axis_helpers.rb', line 122

def order_of_magnitude(value)
  return 0 if value.nil? || value.zero?
  magnitude = Math.log10 value
  order_of_magnitude = magnitude.floor
  order_of_magnitude.zero? ? 1 : order_of_magnitude
end

#ordinate_scale(data) ⇒ Object

Calculates the number of steps and the step width for ordinate axis labels. The ordinate axis is assumed to start at 0.

data - an Array of Numerics.

Returns a Hash with:

:scaleSteps      - the number of steps (always <= 10)
:scaleStepWidth  - the value jump between steps
:scaleStartValue - 0



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# File 'lib/chartjs/axis_helpers.rb', line 26

def ordinate_scale(data)
  scale_max = calculate_scale_max data.max
  normalised_scale_max = normalise scale_max

  # normalised_scale_max  number_steps  step_width
  #          0                 0           0
  #          0.5               5           1
  #          1                 5           2
  #          1.5               5           3
  #          2                 4           5
  #          2.5               5           5
  #          3                 6           5
  #          3.5               7           5
  #          4                 8           5
  #          4.5               9           5
  #          5                10           5
  #          5.5               6          10
  #          6                 6          10
  #          6.5               7          10
  #          7                 7          10
  #          7.5               8          10
  #          8                 8          10
  #          8.5               9          10
  #          9                 9          10
  #          9.5              10          10
  if normalised_scale_max.zero?
    number_steps = 0
    step_width = 0
  elsif normalised_scale_max < 2
    number_steps = 5
    step_width = scale_max / number_steps
  elsif normalised_scale_max < 5.5
    step_width = 5 * 10**(order_of_magnitude(scale_max) - 1)
    number_steps = scale_max / step_width.to_f
  else
    step_width = 10**(order_of_magnitude(scale_max))
    number_steps = scale_max / step_width.to_f
  end

  {scaleSteps: number_steps.ceil, scaleStepWidth: step_width, scaleStartValue: 0}
end

#series(data) ⇒ Object

Returns an ordered copy of data with “missing” keys mapped to 0 values.

data - a Hash of Integer keys mapped to to Integer values.

Returns an OrderedHash whose Integer keys run from 0 to data’s maximum key and whose values are the corresponding values in data or 0.



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# File 'lib/chartjs/axis_helpers.rb', line 12

def series(data)
  return {} if data.nil? || data.empty?
  (0..data.keys.max).reduce(ActiveSupport::OrderedHash.new) { |hash,k| hash[k] = data[k] || 0; hash }
end