"how to properly use file_exists with branch operator?"

Hi @kayman,

A priori, you have to set the "absolute path" of your file (including the extension) in the condition value parameter of the Branch operator.
Take a look at this process : 

<?xml version="1.0" encoding="UTF-8"?><process version="9.1.000">
  <context>
    <input/>
    <output/>
    <macros/>
  </context>
  <operator activated="true" class="process" compatibility="9.1.000" expanded="true" name="Process">
    <parameter key="logverbosity" value="init"/>
    <parameter key="random_seed" value="2001"/>
    <parameter key="send_mail" value="never"/>
    <parameter key="notification_email" value=""/>
    <parameter key="process_duration_for_mail" value="30"/>
    <parameter key="encoding" value="SYSTEM"/>
    <process expanded="true">
      <operator activated="true" class="operator_toolbox:create_exampleset" compatibility="1.7.000" expanded="true" height="68" name="Create ExampleSet" width="90" x="112" y="85">
        <parameter key="generator_type" value="comma_separated_text"/>
        <parameter key="number_of_examples" value="100"/>
        <parameter key="use_stepsize" value="false"/>
        <list key="function_descriptions"/>
        <parameter key="add_id_attribute" value="false"/>
        <list key="numeric_series_configuration"/>
        <list key="date_series_configuration"/>
        <list key="date_series_configuration (interval)"/>
        <parameter key="date_format" value="yyyy-MM-dd HH:mm:ss"/>
        <parameter key="input_csv_text" value="Id,Att1&#10;1,1&#10;2,2&#10;3,3&#10;4,4"/>
        <parameter key="column_separator" value=","/>
        <parameter key="parse_all_as_nominal" value="false"/>
        <parameter key="decimal_point_character" value="."/>
        <parameter key="trim_attribute_names" value="true"/>
      </operator>
      <operator activated="true" class="concurrency:loop_files" compatibility="9.1.000" expanded="true" height="82" name="Loop Files" width="90" x="246" y="85">
        <parameter key="directory" value="C:\Users\Lionel\Documents\Formations_DataScience\Rapidminer\Ambassador_Role"/>
        <parameter key="filter_type" value="glob"/>
        <parameter key="filter_by_glob" value="*.docx"/>
        <parameter key="filter_by_regex" value="*docx"/>
        <parameter key="recursive" value="false"/>
        <parameter key="enable_macros" value="false"/>
        <parameter key="macro_for_file_name" value="file_name"/>
        <parameter key="macro_for_file_type" value="file_type"/>
        <parameter key="macro_for_folder_name" value="folder_name"/>
        <parameter key="reuse_results" value="true"/>
        <parameter key="enable_parallel_execution" value="true"/>
        <process expanded="true">
          <operator activated="true" class="branch" compatibility="9.1.000" expanded="true" height="103" name="Branch" width="90" x="313" y="34">
            <parameter key="condition_type" value="file_exists"/>
            <parameter key="condition_value" value="C:\Users\Lionel\Documents\Formations_DataScience\Rapidminer\Ambassador_Role\Process.docx"/>
            <parameter key="expression" value=""/>
            <parameter key="io_object" value="ANOVAMatrix"/>
            <parameter key="return_inner_output" value="true"/>
            <process expanded="true">
              <operator activated="true" class="generate_attributes" compatibility="9.1.000" expanded="true" height="82" name="Generate Attributes" width="90" x="179" y="136">
                <list key="function_descriptions">
                  <parameter key="Att2" value="2*Att1"/>
                </list>
                <parameter key="keep_all" value="true"/>
              </operator>
              <connect from_port="condition" to_port="input 1"/>
              <connect from_port="input 1" to_op="Generate Attributes" to_port="example set input"/>
              <connect from_op="Generate Attributes" from_port="example set output" to_port="input 2"/>
              <portSpacing port="source_condition" spacing="0"/>
              <portSpacing port="source_input 1" spacing="0"/>
              <portSpacing port="source_input 2" spacing="0"/>
              <portSpacing port="sink_input 1" spacing="0"/>
              <portSpacing port="sink_input 2" spacing="0"/>
              <portSpacing port="sink_input 3" spacing="0"/>
            </process>
            <process expanded="true">
              <operator activated="true" class="generate_attributes" compatibility="9.1.000" expanded="true" height="82" name="Generate Attributes (2)" width="90" x="179" y="85">
                <list key="function_descriptions">
                  <parameter key="Att2" value="0"/>
                </list>
                <parameter key="keep_all" value="true"/>
              </operator>
              <connect from_port="condition" to_port="input 1"/>
              <connect from_port="input 1" to_op="Generate Attributes (2)" to_port="example set input"/>
              <connect from_op="Generate Attributes (2)" from_port="example set output" to_port="input 2"/>
              <portSpacing port="source_condition" spacing="0"/>
              <portSpacing port="source_input 1" spacing="0"/>
              <portSpacing port="source_input 2" spacing="0"/>
              <portSpacing port="sink_input 1" spacing="0"/>
              <portSpacing port="sink_input 2" spacing="0"/>
              <portSpacing port="sink_input 3" spacing="0"/>
            </process>
          </operator>
          <connect from_port="file object" to_op="Branch" to_port="condition"/>
          <connect from_port="input 1" to_op="Branch" to_port="input 1"/>
          <connect from_op="Branch" from_port="input 2" to_port="output 1"/>
          <portSpacing port="source_file object" spacing="0"/>
          <portSpacing port="source_input 1" spacing="0"/>
          <portSpacing port="source_input 2" spacing="0"/>
          <portSpacing port="sink_output 1" spacing="0"/>
          <portSpacing port="sink_output 2" spacing="0"/>
        </process>
      </operator>
      <connect from_op="Create ExampleSet" from_port="output" to_op="Loop Files" to_port="input 1"/>
      <connect from_op="Loop Files" from_port="output 1" 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>

Bummer...

Seems like it's not working indeed if I use the 'windows user path logic' (which would have been /Documents/Formations_DataScience in your example), while ok if I use the C:\ path logic. I prefer the first one since it makes it equal to my Linux server environment and then I could have kept it simple. 

Anyway, happy holidays for you also !