<p>Here's what I tried to do to play with it:</p>

<pre><code>$ bin/mlpack_preprocess_split -i ~/datasets/corel.csv -I ~/datasets/corel.csv -t corel-train.csv -T corel-test.csv -v
[DEBUG] Compiled with debugging symbols.
[WARN ] You did not specify --training_labels_file, so the trainingset labels file name will be automatically set to 'train_/home/ryan/datasets/corel.csv'.
[WARN ] You did not specify --test_labels_file, so the test set labels file name will be automatically set to 'test_/home/ryan/datasets/corel.csv'.
[WARN ] You did not specify --test_ratio, so it will be automatically set to 0.2.
[INFO ] Loading '/home/ryan/datasets/corel.csv' as CSV data.  Size is 32 x 37749.
[INFO ] Loading '/home/ryan/datasets/corel.csv' as CSV data.  Size is 32 x 37749.
[INFO ] Training data contains 30200 points.
[INFO ] Test data contains 7549 points.
[INFO ] Saving CSV data to 'corel-train.csv'.
[INFO ] Saving CSV data to 'corel-test.csv'.
[WARN ] Cannot open file 'train_/home/ryan/datasets/corel.csv' for writing; save failed.
[WARN ] Cannot open file 'test_/home/ryan/datasets/corel.csv' for writing; save failed.
[INFO ] 
[INFO ] Execution parameters:
[INFO ]   help: false
[INFO ]   info: ""
[INFO ]   input_file: /home/ryan/datasets/corel.csv
[INFO ]   input_labels_file: /home/ryan/datasets/corel.csv
[INFO ]   test_file: corel-test.csv
[INFO ]   test_labels_file: ""
[INFO ]   test_ratio: 0.2
[INFO ]   training_file: corel-train.csv
[INFO ]   training_labels_file: ""
[INFO ]   verbose: true
[INFO ]   version: false
[INFO ] 
[INFO ] Program timers:
[INFO ]   loading_data: 1.012701s
[INFO ]   saving_data: 0.530123s
[INFO ]   total_time: 1.631944s
</code></pre>

<p>So I guess, we need to be more careful with prepending "train_", we have to do it in the right place.  Maybe some string tokenization is necessary. :(</p>

<p>Also, Keon, I made a few formatting and documentation changes in <a href="https://github.com/mlpack/mlpack/commit/6a94eb6efb37eca09e95fd53bd7c21334abf7614" class="commit-link"><tt>6a94eb6</tt></a>, please let me know if I broke anything.</p>

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