title: How to convert csv to multiMap in java?
body: <p>I'm dealing with some data like the following, the first column is the trade id, the second column is the simulation id(duplicate a lot), the third column is some stupid date also quite duplicated, the forth one is the present value of a trade, mostly it is just 0, but any other value should be quite unique.</p>
  
  <pre><code>41120634|1554|20150203|-509057.56
  40998001|1554|20150203|0
  40960705|1554|20150203|0
  40998049|1554|20150203|0
  41038826|1554|20150203|0
  41081136|1554|20150203|-7198152.23
  41120653|1554|20150203|-319.436349
  41081091|1554|20150203|-4.28520907E+009
  </code></pre>
  
  <p>I've decided to use a data structure as follows:</p>
  
  <pre><code>Map&lt;Integer,Map&lt;Integer,List&lt;Map&lt;Integer,Float&gt;&gt;&gt;
  </code></pre>
  
  <p>Then my csv will be saved like:</p>
  
  <pre><code> {20150203:{1554:[{41120634:-509057.56,41120634:0,...}]}}
  </code></pre>
  
  <p>My question is how to convert such a csv file to my intended data structure efficiently?</p>