title: Impute missing value error in rapidminer
body: <p>I have a sample data of some students in with <strong>subjects</strong>, <strong>grades</strong>, <strong>semester</strong> column values. In this data set I have some missing values in <strong>semester</strong> column, I need to impute those missing values by learning the existing values in <strong>semester</strong> column. For this I am using <strong>Rapid Miner</strong>, see the below image in which I am using 2 processes of retrieve data and impute that data, <a href="https://i.stack.imgur.com/WSklY.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WSklY.png" alt="Processes"></a> </p>
  
  <p>when I try to execute the flow it shows me below error:
  <a href="https://i.stack.imgur.com/jjmQv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jjmQv.png" alt="ERROR"></a></p>
  
  <p>I tried to change the data type of <strong>semester</strong> column from numerical to real also but no success, there is no such kind of solution on the web too, can anyone have suggestions?</p>
  
  <p><strong>UPDATED</strong>
  Below is the XML:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;&lt;process version="8.1.001"&gt;
    &lt;context&gt;
     &lt;input/&gt;
     &lt;output/&gt;
     &lt;macros/&gt;
    &lt;/context&gt;
    &lt;operator activated="true" class="process" compatibility="8.1.001" expanded="true" name="Process"&gt;
    &lt;process expanded="true"&gt;
    &lt;operator activated="true" class="retrieve" compatibility="8.1.001" expanded="true" height="68" name="Retrieve" width="90" x="179" y="85"&gt;
    &lt;parameter key="repository_entry" value="//Local Repository/testing data 2"/&gt;
    &lt;/operator&gt;
    &lt;operator activated="true" class="impute_missing_values" compatibility="8.1.001" expanded="true" height="68" name="Impute Missing Values" width="90" x="380" y="85"&gt;
      &lt;parameter key="attribute_filter_type" value="single"/&gt;
      &lt;parameter key="attribute" value="Semester"/&gt;
      &lt;parameter key="attributes" value="Subjects|Semester|Grades|GPA|Course Code|Batch"/&gt;
      &lt;process expanded="true"&gt;
        &lt;connect from_port="example set source" to_port="model sink"/&gt;
        &lt;portSpacing port="source_example set source" spacing="0"/&gt;
        &lt;portSpacing port="sink_model sink" spacing="0"/&gt;
      &lt;/process&gt;
    &lt;/operator&gt;
    &lt;connect from_op="Retrieve" from_port="output" to_op="Impute Missing Values" to_port="example set in"/&gt;
    &lt;connect from_op="Impute Missing Values" from_port="example set out" to_port="result 1"/&gt;
    &lt;portSpacing port="source_input 1" spacing="0"/&gt;
    &lt;portSpacing port="sink_result 1" spacing="0"/&gt;
    &lt;portSpacing port="sink_result 2" spacing="0"/&gt;
    &lt;description align="center" color="yellow" colored="false" height="105" resized="false" width="180" x="158" y="110"&gt;Type your comment&lt;/description&gt;
      &lt;/process&gt;
    &lt;/operator&gt;
  &lt;/process&gt;
  </code></pre>
  
  <p>One more thing is when I run the process along with the above error I can see the resulted output by clicking the result output icon as below:</p>
  
  <p><a href="https://i.stack.imgur.com/uMDtW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uMDtW.png" alt="Get output data"></a></p>
  
  <p>I have total of 54 records in my file out of which 7 are missing values in <strong>semester</strong> column, and resulted output shows 47 records, it removes those missing values records, should these missing values be replaced with some other value??why it is removing those records??</p>