Why I like JRuby
November 7th, 2008
No comments
Some days ago Tom forwarded me an email from Mikael Lammentausta. Mikael found an issue with rmagick4j. Using this Mikael's script
RUBY:
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require 'rubygems'
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require 'gruff'
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def basic_graph()
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g = Gruff::Line.new
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g.theme = {
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:colors => ['#7F0099', '#2F85ED', '#2FED09','#EC962F'],
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:marker_color => '#aaa',
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:background_colors => ['#E8E8E8','#B9FD6C']
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}
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g.hide_title = true
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g.legend_font_size = 12
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g.marker_font_size = 16
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g.hide_dots = false
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return g
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end
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def bmi(params={})
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g = basic_graph()
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g.y_axis_label = 'BMI'
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bmis = [24.3, 23.9, 23.7, 23.7, 23.6, 23.9, 23.6, 23.7, 23.4, 23.4, 23.4, 22.9]
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g.data( 'BMI', bmis )
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g.hide_legend = true
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return g
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end
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g=bmi
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g.write 'graph.jpg'
You get two different outputs.
MRI-generated
JRuby
As you may see, the numbers are wrong in JRuby... or not.
Looking at gruff code, I saw the problem was in the label method.
RUBY:
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def label(value)
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if (@spread.to_f % @marker_count.to_f == 0) || !@y_axis_increment.nil?
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return value.to_i.to_s
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end
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if @spread> 10.0
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sprintf("%0i", value)
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elsif @spread>= 3.0
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sprintf("%0.2f", value)
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else
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value.to_s
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end
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end
The problem can be found in line 10. With a right input, you can make
RUBY:
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(@spread.to_f % @marker_count.to_f == 0) || !@y_axis_increment.nil?
false and have a @spread < 3.0. Then look at this code:
RUBY:
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i = 23.599999999999998
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puts i
In JRuby, you get what you expect 23.599999999999998 but, in MRI, you get 23.6. So, that was the problem. JRuby is more precise than MRI.
NOTE:
jruby 1.1.5 (ruby 1.8.6 patchlevel 114) (2008-11-03 rev 7996) [i386-java]
ruby 1.8.6 (2008-03-03 patchlevel 114) [universal-darwin9.0]
