The method run(JavaRDD<Sequence>) is not applicable for the arguments (JavaRDD<List<String>>)

Question

When trying to execute the Prefixspan algo in the spark mllib I get the error

The method run(JavaRDD Sequence ) in the type PrefixSpan is not applicable >for the arguments (JavaRDD List String)

The code I see on the website is

JavaRDD<List<List<Integer>>> sequences = sc.parallelize(Arrays.asList(
Arrays.asList(Arrays.asList(1, 2), Arrays.asList(3)),
Arrays.asList(Arrays.asList(1), Arrays.asList(3, 2), Arrays.asList(1, 2)),
Arrays.asList(Arrays.asList(1, 2), Arrays.asList(5)),
Arrays.asList(Arrays.asList(6))), 2);
PrefixSpan prefixSpan = new PrefixSpan().setMinSupport(0.5).setMaxPatternLength(5);
PrefixSpanModel<Integer> model = prefixSpan.run(sequences);
for (PrefixSpan.FreqSequence<Integer> freqSeq: model.freqSequences().toJavaRDD().collect()) {
     System.out.println(freqSeq.javaSequence() + ", " + freqSeq.freq());
}

My code is

List<List<String>> sequences = createLists(featuresForAlgo);

JavaRDD<List<String>> rdd =  sc.parallelize(sequences);

PrefixSpan prefixSpan = new PrefixSpan()
          .setMinSupport(0.5)
          .setMaxPatternLength(5);
        PrefixSpanModel<String> model = prefixSpan.run(rdd);
        for (PrefixSpan.FreqSequence<Integer> freqSeq: model.freqSequences().toJavaRDD().collect()) {
          System.out.println(freqSeq.javaSequence() + ", " + freqSeq.freq());
        }

Where the method prefixSpan.run(rdd) gives the error. Any idea why I get this error? As far as I know a List is a sequence.

Thanks

Answer 1

The error is slightly misleading but if you see the source code of PrefixSpan class you will find that run method parameter is like

@param data ordered sequences of itemsets stored as Java Iterable of Iterables

So prefixSpan.run method needs JavaRDD<List<List<String>>> . In your code you can do like

List<List<List<String>>> seqNew = new ArrayList<List<List<String>>>();
seqNew.add(sequences);
JavaRDD<List<List<String>>> rdd =  sc.parallelize(seqNew);