Question

I have an array of hashes which look like:

ward = {id: id, name: record["Externalization"], mnemonic: record["Mnemonic"],
   seqno: record["SeqNo"]}

All fields are strings.

Now I want to sort them first on seqno and then on name. seqno can be nil (if seqno is nil, then this ward must come after the ones having a seqno).

What I have so far is:

wardList.sort! do |a,b| 
  return (a[:name] <=> b[:name]) if (a[:seqno].nil? && b[:seqno].nil?) 
  return -1 if a[:seqno].nil?
  return 1 if b[:seqno].nil?
  (a[:seqno] <=> b[:seqno]).nonzero? ||
    (a[:name] <=> b[:name])
end

But this gives me the error: can’t convert Symbol into Integer

Answer 1

First, normalize your data, you can’t work with integers as strings here:

wardList = wardList.map { |x| x.merge({:id    => x[:id].to_i, 
                                       :seqno => x[:seqno].try(:to_i) }) }

Then you can use sort_by, which supports lexicographical sorting:

wardList.sort_by! { |x| [x[:seqno] || Float::INFINITY, x[:name]] }

Example:

irb(main):034:0> a = [{:seqno=>5, :name=>"xsd"}, 
                      {:seqno=>nil, :name=>"foo"}, 
                      {:seqno=>nil, :name=>"bar"}, 
                      {:seqno=>1, :name=>"meh"}]
irb(main):033:0> a.sort_by { |x| [x[:seqno] || Float::INFINITY, x[:name]] }
=> [{:seqno=>1, :name=>"meh"},
    {:seqno=>5, :name=>"xsd"},
    {:seqno=>nil, :name=>"bar"},
    {:seqno=>nil, :name=>"foo"}]