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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-9664) FlinkML Quickstart Loading Data section example doesn't work as described
Date Tue, 14 Aug 2018 10:14:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-9664?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16579596#comment-16579596

ASF GitHub Bot commented on FLINK-9664:

zentol closed pull request #6425: [FLINK-9664][Doc] fixing documentation in ML quick start
URL: https://github.com/apache/flink/pull/6425

This is a PR merged from a forked repository.
As GitHub hides the original diff on merge, it is displayed below for
the sake of provenance:

As this is a foreign pull request (from a fork), the diff is supplied
below (as it won't show otherwise due to GitHub magic):

diff --git a/docs/dev/libs/ml/quickstart.md b/docs/dev/libs/ml/quickstart.md
index ea6f8049755..e056b28b505 100644
--- a/docs/dev/libs/ml/quickstart.md
+++ b/docs/dev/libs/ml/quickstart.md
@@ -129,15 +129,14 @@ and the [test set here](http://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/b
 This is an astroparticle binary classification dataset, used by Hsu et al. [[3]](#hsu) in
 practical Support Vector Machine (SVM) guide. It contains 4 numerical features, and the class
-We can simply import the dataset then using:
+We can simply import the dataset using:
 {% highlight scala %}
 import org.apache.flink.ml.MLUtils
-val astroTrain: DataSet[LabeledVector] = MLUtils.readLibSVM(env, "/path/to/svmguide1")
-val astroTest: DataSet[(Vector, Double)] = MLUtils.readLibSVM(env, "/path/to/svmguide1.t")
-      .map(x => (x.vector, x.label))
+val astroTrainLibSVM: DataSet[LabeledVector] = MLUtils.readLibSVM(env, "/path/to/svmguide1")
+val astroTestLibSVM: DataSet[LabeledVector] = MLUtils.readLibSVM(env, "/path/to/svmguide1.t")
 {% endhighlight %}
@@ -146,7 +145,23 @@ create a classifier.
 ## Classification
-Once we have imported the dataset we can train a `Predictor` such as a linear SVM classifier.
+After importing the training and test dataset, they need to be prepared for the classification.

+Since Flink SVM only supports threshold binary values of `+1.0` and `-1.0`, a conversion
+needed after loading the LibSVM dataset because it is labelled using `1`s and `0`s.
+A conversion can be done using a simple normalizer mapping function:
+{% highlight scala %}
+def normalizer : LabeledVector => LabeledVector = { 
+    lv => LabeledVector(if (lv.label > 0.0) 1.0 else -1.0, lv.vector)
+val astroTrain: DataSet[LabeledVector] = astroTrainLibSVM.map(normalizer)
+val astroTest: DataSet[(Vector, Double)] = astroTestLibSVM.map(normalizer).map(x => (x.vector,
+{% endhighlight %}
+Once we have converted the dataset we can train a `Predictor` such as a linear SVM classifier.
 We can set a number of parameters for the classifier. Here we set the `Blocks` parameter,
 which is used to split the input by the underlying CoCoA algorithm [[2]](#jaggi) uses. The
 regularization parameter determines the amount of $l_2$ regularization applied, which is


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> FlinkML Quickstart Loading Data section example doesn't work as described
> -------------------------------------------------------------------------
>                 Key: FLINK-9664
>                 URL: https://issues.apache.org/jira/browse/FLINK-9664
>             Project: Flink
>          Issue Type: Bug
>          Components: Documentation, Machine Learning Library
>    Affects Versions: 1.5.0
>            Reporter: Mano Swerts
>            Assignee: Rong Rong
>            Priority: Major
>              Labels: documentation-update, machine_learning, ml, pull-request-available
>             Fix For: 1.7.0
>   Original Estimate: 1h
>  Remaining Estimate: 1h
> The ML documentation example isn't complete: [https://ci.apache.org/projects/flink/flink-docs-release-1.5/dev/libs/ml/quickstart.html#loading-data]
> The referred section loads data from an astroparticle binary classification dataset
to showcase SVM. The dataset uses 0 and 1 as labels, which doesn't produce correct results.
The SVM predictor expects -1 and 1 labels to correctly predict the label. The documentation,
however, doesn't mention that. The example therefore doesn't work without a clue why.
> The documentation should be updated with an explicit mention to -1 and 1 labels and a
mapping function that shows the conversion of the labels.

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