Delete hyphen (special chars) while processing text in RapidMiner

Question

I would like to delete all hyphens in the text document which I analyze in Rapidminer. For that I use operator "Process documents from files" to analyze large PDF-files. Each file contains a lot of hyphens which I would like to delete before I'll tokenize the text into pieces (non letters). I've used operator "Replace token". With it I can replace hyphens with other symbols, but I cannot replace them with nothing or empty string(" "). I've tried also to use my own customized dictionary of stopwords(non-letters, -). This operator does no work at all. I've saved my dictionary containing the chars and words I want to delete as a text file (each in the new line). Can anybody help on this issue?

Answer 1

You can use Replace Tokens with the following parameters.

replace what ()[-]

replace by $1

It's a bit of a hack but it works because the first capturing group between the brackets will always be empty and the whole regular expression will match a single hyphen. The $1 is the result of the first capture group and it's always empty.

Here's an example process that shows this working.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<process version="7.0.000">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="7.0.000" expanded="true" name="Process">
    <process expanded="true">
      <operator activated="true" class="text:create_document" compatibility="7.0.000" expanded="true" height="68" name="Create Document" width="90" x="246" y="187">
        <parameter key="text" value="some text &#10;with&#10;some-text-with-hyphens-in&#10;hyphens in&#10;"/>
      </operator>
      <operator activated="true" class="text:replace_tokens" compatibility="7.0.000" expanded="true" height="68" name="Replace Tokens" width="90" x="447" y="187">
        <list key="replace_dictionary">
          <parameter key="()[-]" value="$1"/>
        </list>
      </operator>
      <operator activated="true" class="text:process_documents" compatibility="7.0.000" expanded="true" height="103" name="Process Documents" width="90" x="648" y="187">
        <parameter key="vector_creation" value="Term Occurrences"/>
        <process expanded="true">
          <operator activated="true" class="text:tokenize" compatibility="7.0.000" expanded="true" height="68" name="Tokenize" width="90" x="179" y="85"/>
          <connect from_port="document" to_op="Tokenize" to_port="document"/>
          <connect from_op="Tokenize" from_port="document" to_port="document 1"/>
          <portSpacing port="source_document" spacing="0"/>
          <portSpacing port="sink_document 1" spacing="0"/>
          <portSpacing port="sink_document 2" spacing="0"/>
        </process>
      </operator>
      <connect from_op="Create Document" from_port="output" to_op="Replace Tokens" to_port="document"/>
      <connect from_op="Replace Tokens" from_port="document" to_op="Process Documents" to_port="documents 1"/>
      <connect from_op="Process Documents" from_port="example set" to_port="result 1"/>
      <portSpacing port="source_input 1" spacing="0"/>
      <portSpacing port="sink_result 1" spacing="0"/>
      <portSpacing port="sink_result 2" spacing="0"/>
    </process>
  </operator>
</process>

Hope that helps as a basis.