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POturn list of depth first traversal nodes back into tree structure in Ruby
 

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  1. POturn list of depth first traversal nodes back into tree structure in Ruby
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    <p>Given the following input (from a CSV file):</p> <pre><code>input = [ { :level =&gt; 0, :value =&gt; "a" }, { :level =&gt; 1, :value =&gt; "1" }, { :level =&gt; 1, :value =&gt; "2" }, { :level =&gt; 2, :value =&gt; "I" }, { :level =&gt; 2, :value =&gt; "II" }, { :level =&gt; 2, :value =&gt; "III" }, { :level =&gt; 0, :value =&gt; "b" }, { :level =&gt; 0, :value =&gt; "c" }, { :level =&gt; 0, :value =&gt; "d" }, { :level =&gt; 1, :value =&gt; "3" }, { :level =&gt; 1, :value =&gt; "4" }, ] </code></pre> <p>How can I convert this to the following in "The Ruby Way":</p> <pre><code>expected = [ { :value =&gt; "a", :children =&gt; [ { :value =&gt; 1, :children =&gt; nil }, { :value =&gt; 2, :children =&gt; [ { :value =&gt; "I", :children =&gt; nil }, { :value =&gt; "II", :children =&gt; nil }, { :value =&gt; "III", :children =&gt; nil } ] } ] }, { :value =&gt; "b", :children =&gt; nil }, { :value =&gt; "c", :children =&gt; nil }, { :value =&gt; "d", :children =&gt; [ { :value =&gt; 3, :children =&gt; nil }, { :value =&gt; 4, :children =&gt; nil } ] }, ] </code></pre> <p>?</p> <p><strong>Edited:</strong></p> <p>My solution to this was to sidestep the problem, transform it and get someone else to solve it:</p> <pre><code>require 'yaml' def linear_to_tree(a) yaml_lines = [] a.each do |el| indent = " " * 4 * el[:level] yaml_lines &lt;&lt; "#{indent}-" yaml_lines &lt;&lt; "#{indent} :value: #{(el[:value])}" yaml_lines &lt;&lt; "#{indent} :children:" end yaml_lines &lt;&lt; "" # without this, YAML.load complains yaml = yaml_lines.join("\n") # open("test_yaml.txt", "w"){|f| f.write(yaml)} YAML.load(yaml) end </code></pre> <p>But there must be a more elegant way to solve this.</p> <p>P.S. I'd also like to see a one-liner for this transformation, just to see if it's possible.</p>
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    1. CONo, __someone else__ is the `Yaml` parser.
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    2. COso these are basically ordered in "depth first" order?
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    3. COYes. (At least I think so from what I've seen of the CSV.)
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