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From Denis Magda <dma...@apache.org>
Subject Fwd: NPE exception in KMeansTrainer
Date Tue, 21 Aug 2018 04:11:03 GMT
Hey, ML experts,

Here is an ML issue reported. Please have a look.

--
Denis

---------- Forwarded message ---------
From: DocDVZ <docdvz@gmail.com>
Date: Mon, Aug 20, 2018 at 10:53 AM
Subject: NPE exception in KMeansTrainer
To: <user@ignite.apache.org>


Hello,

Since I'm new to data science, I'm not really sure if it's a bug or wrong
incoming data, so I decided to ask here for advice before submitting a
ticket. I tried to apply Kmeans algorithm on my bag-of-words data with ~8k
features. So I copy-pasted some lines from example:

        IgniteCache<String, double[]> dataCache = ignite.cache(storageName);
        KMeansTrainer trainer = new KMeansTrainer().withSeed(1234L);
        KMeansModel mdl = trainer.fit(
                ignite,
                dataCache,
                (k, v) -> Arrays.copyOfRange(v, 1, v.length),
                (k, v) -> v[0]
        );

But this leads to a NullPointerException in KMeansTrainer.class:

Caused by: java.lang.NullPointerException
        at
org.apache.ignite.ml
.clustering.kmeans.KMeansTrainer.lambda$initClusterCentersRandomly$4dba08e1$1(KMeansTrainer.java:190)
        at
org.apache.ignite.ml.dataset.impl.cache.CacheBasedDataset.computeForAllPartitions(CacheBasedDataset.java:158)
        at
org.apache.ignite.ml.dataset.impl.cache.CacheBasedDataset.compute(CacheBasedDataset.java:122)
        at org.apache.ignite.ml.dataset.Dataset.compute(Dataset.java:102)
        at org.apache.ignite.ml.dataset.Dataset.compute(Dataset.java:156)
        at
org.apache.ignite.ml
.clustering.kmeans.KMeansTrainer.initClusterCentersRandomly(KMeansTrainer.java:186)
        at
org.apache.ignite.ml
.clustering.kmeans.KMeansTrainer.fit(KMeansTrainer.java:86)


at line:

        List<LabeledVector> rndPnts = dataset.compute(data -> {
            List<LabeledVector> rndPnt = new ArrayList<>();
            rndPnt.add(data.getRow(new
Random(seed).nextInt(data.rowSize())));
            return rndPnt;
        }, (a, b) -> a == null ? b : Stream.concat(a.stream(),
b.stream()).collect(Collectors.toList()));

The reducer receives null value for b and since there's no check for null,
b.stream() leads to NPE. Ignite version is 2.6. This seems like a bug for
me, is there any ways to workaround this issue?



--
Sent from: http://apache-ignite-users.70518.x6.nabble.com/

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