Sort an array of objects in ruby using "sort"

Question

How can I sort this array so all hashes with optional = true are last?

my_array = [
  { name: "foo", optional: true }, 
  { name: "pop" }, 
  { name: "boop", optional: true },
  { name: "pop", optional: false }
]

I tried this:

my_array.sort { |a,b| a['optional'] <=> b['optional'] }

But I get this error:

comparison of Hash with Hash failed

Error is surprising since doing a['optional'] would return a value of true, false, or nil.

Note:
I am aware of this solution .sort_by { |a| (a['optional'] ? 1 : 0) }. I would like to understand the sort method in particular.

Mureinik · Accepted Answer · 2015-09-25 08:35:50Z

6

Booleans are not ordinal data types - true is not larger or smaller than false, it's just not equal, so you can't use the <=> operator either. If you want to sort the array according to the optional property, you'd need some simple custom logic. E.g.:

my_array.sort { |a,b| a['optional'] == b['optional'] ? 0 : a['optional'] ? 1 : -1}

answered Sep 25, 2015 at 8:35

Mureinik

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Comments

Michael Kohl · Accepted Answer · 2015-09-25 10:18:45Z

1

For sort to work, you have to implement the block according to the documentation:

The block must implement a comparison between a and b, and return -1, when a follows b, 0 when a and b are equivalent, or +1 if b follows a.

@Mureinik already showed you how to do that.

Personally I'd recommend using sort_by, since that's basically exactly the use case it was made for.

answered Sep 25, 2015 at 10:18

Michael Kohl

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