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POTo Use or Not to Use Data.Map
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copied!<p>I'm currently working on a Haskell API. The latter provides some functions that currently take a <em>list of lists</em> as input, i.e. <code>[(String,[(String, Double)])]</code>.</p> <p>For visualization purposes, here's a sample of the <em>list of lists</em> mentioned above: </p> <pre><code>[ ("A", [ ("I1", 1), ("I2", 2), ] ), ("B", [ ("I1", 3), ] ) ] </code></pre> <p>I've defined some <em>private</em> helper functions. One helper function will search for specific entries in this list (<code>Data.List.find</code> = <code>O(n)</code>); another one will perform intersections; and another function will transform the list presented above to the following one:</p> <pre><code>[ ("I1", [ ("A", 1), ("B", 3), ] ), ("I2", [ ("A", 2), ] ) ] </code></pre> <p>The function that performs the transformation uses <code>Data.Map</code>, since it offers some functions that simplify that process a lot, like <code>Data.Map.unionWith</code> and <code>Data.Map.insertWith</code>. Well, since the transformation function had to call <code>Data.Map.fromList</code> and <code>Data.Map.toList</code>, I thought it would be nice to have a <em>map of maps</em> instead of a <em>list of lists</em> from the beginning. And so I changed my sample input to match the <em>map of maps</em> requirement. </p> <p>Again, for visualization purposes, here's the list from above as a <em>map of maps</em>: </p> <pre><code>Map.fromList [ ("A", Map.fromList [ ("I1", 1), ("I2", 2), ] ), ("B", Map.fromList [ ("I1", 3), ] ) ] </code></pre> <p>Thanks to this step my code lost a few lines, and thanks to <code>Data.Map.lookup</code>, finding a desired now only takes <code>O(log n)</code> time.</p> <p>Nonetheless, I'm currently asking myself if this really is a good solution? Is a <em>map of maps</em> the way to go? Or should the transformation function work with <code>Data.Map.fromList</code> and <code>Data.Map.toList</code>, and let the rest work with <em>list of lists</em>? Or better yet, is there a data structure that is more suitable for this kind of work?</p> <p>I'm really looking forward to your replies.</p>

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