Mark Needham

Thoughts on Software Development

Ruby: Sorting by boolean fields

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We were doing a bit of work on RapidFTR in the ThoughtWorks Pune office today and one problem my pair and I were trying to solve was how to sort a collection of objects by a boolean field.

Therefore given the following array of values:

form_sections = [FormSection.new(:enabled => false, :name => "a", :order => 1), 
                 FormSection.new(:enabled => true, :name => "b", :order => 2)]

We wanted to display those form sections which were disabled at the bottom of the page.

We originally tried the following:

form_sections.sort_by { |row| [row.enabled, row.order] }

But got the following error:

undefined method `<=>' for true:TrueClass

We figured we’d need to convert the true and false values to equivalent values which is demonstrated on this Stack Overflow post:

form_sections.sort_by { |row| [row.enabled ? 0 : 1, row.order] }

I didn’t realise it would be that simple to do – it’s pretty neat.

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Written by Mark Needham

January 8th, 2011 at 1:15 pm

Posted in Ruby

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