title: appending two files in Weka
body: <p>I have two datasets. Basically, they are two .arff file.</p>
  <p>Fold1.arff contains:</p>
  <pre><code>@relation iris
  
  @attribute sepallength numeric
  @attribute sepalwidth numeric
  @attribute petallength numeric
  @attribute petalwidth numeric
  @attribute class {Iris-setosa,Iris-versicolor,Iris-virginica}
  
  @data
  5.1,3.5,1.4,0.2,Iris-setosa
  5.4,3.7,1.5,0.2,Iris-setosa
  5.4,3.4,1.7,0.2,Iris-setosa
  4.8,3.1,1.6,0.2,Iris-setosa
  5,3.5,1.3,0.3,Iris-setosa
  7,3.2,4.7,1.4,Iris-versicolor
  5,2,3.5,1,Iris-versicolor
  5.9,3.2,4.8,1.8,Iris-versicolor
  5.5,2.4,3.8,1.1,Iris-versicolor
  5.5,2.6,4.4,1.2,Iris-versicolor
  6.3,3.3,6,2.5,Iris-virginica
  6.5,3.2,5.1,2,Iris-virginica
  6.9,3.2,5.7,2.3,Iris-virginica
  7.4,2.8,6.1,1.9,Iris-virginica
  6.7,3.1,5.6,2.4,Iris-virginica
  </code></pre>
  <p>Fold2.arff contains</p>
  <pre><code>@relation iris
  
  @attribute sepallength numeric
  @attribute sepalwidth numeric
  @attribute petallength numeric
  @attribute petalwidth numeric
  @attribute class {Iris-setosa,Iris-versicolor,Iris-virginica}
  
  @data
  4.9,3,1.4,0.2,Iris-setosa
  4.8,3.4,1.6,0.2,Iris-setosa
  5.1,3.7,1.5,0.4,Iris-setosa
  5.4,3.4,1.5,0.4,Iris-setosa
  4.5,2.3,1.3,0.3,Iris-setosa
  6.4,3.2,4.5,1.5,Iris-versicolor
  5.9,3,4.2,1.5,Iris-versicolor
  6.1,2.8,4,1.3,Iris-versicolor
  5.5,2.4,3.7,1,Iris-versicolor
  6.1,3,4.6,1.4,Iris-versicolor
  5.8,2.7,5.1,1.9,Iris-virginica
  6.4,2.7,5.3,1.9,Iris-virginica
  5.6,2.8,4.9,2,Iris-virginica
  7.9,3.8,6.4,2,Iris-virginica
  6.9,3.1,5.1,2.3,Iris-virginica
  </code></pre>
  <p>Now I try to append them using the command:</p>
  <pre><code>java weka.core.Instances append d:\fold1.arff d:\fold2.arff &gt; d:\result.arff
  </code></pre>
  <p>I run the command from the Weka simple CLI field.</p>
  <p>I got this error:</p>
  <pre><code>Usage:
  weka.core.Instances help
      Prints this help
  weka.core.Instances &lt;filename&gt;
      Outputs dataset statistics
  weka.core.Instances merge &lt;filename1&gt; &lt;filename2&gt;
      Merges the datasets (must have same number of rows).
      Generated dataset gets output on stdout.
  weka.core.Instances append &lt;filename1&gt; &lt;filename2&gt;
      Appends the second dataset to the first (must have same number of attributes).
      Generated dataset gets output on stdout.
  weka.core.Instances headers &lt;filename1&gt; &lt;filename2&gt;
      Compares the structure of the two datasets and outputs whether they
      differ or not.
  weka.core.Instances randomize &lt;seed&gt; &lt;filename&gt;
      Randomizes the dataset and outputs it on stdout.
  </code></pre>
  <p>My two files have same number of rows as you can see from the above example. Then why the result.arff file could not create?</p>
  <p>Thank you.</p>