Have something wrong with 'Run mapreduce on a Hadoop Cluster'

Hadoop version 1.2.1 Matlab version 2015a

Linux ubuntu 14.

I install Hadoop with a small cluster(one master and one slave).

It is success to run the example 'wordcount'in Hadoop.

And it is success to read the data from the HDFS through the Matlab.

But when I try to run the example in Matlab 'Run mapreduce on a Hadoop Cluster',I failed.

It shows that,

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

run_mapreduce_on_a_hadoop

ans =

    ArrDelay
    ________

     8      
     8      
    21      
    13      
     4      
    59      
     3      
    11

Parallel mapreduce execution on the Hadoop cluster:

******************************

• MAPREDUCE PROGRESS *

******************************

Map 0% Reduce 0%

Map 100% Reduce 33%

Map 100% Reduce 71%

Map 100% Reduce 100%

Error using mapreduce (line 100)

All the input files must be Sequence files.

Invalid file: ''

Error in run_mapreduce_on_a_hadoop (line 24)

meanDelay = mapreduce(ds,@meanArrivalDelayMapper,@meanArrivalDelayReducer,mr,...

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

There is my Matlab codes

setenv('HADOOP_HOME','/usr/local/hadoop');

cluster = parallel.cluster.Hadoop;

cluster.HadoopProperties('mapred.job.tracker') = 'ubuntu:50031';

cluster.HadoopProperties('fs.default.name') = 'hdfs://ubuntu:8020';

outputFolder = '/home/rjy/logs/hadooplog';

mr = mapreducer(cluster);

ds = datastore('airlinesmall.csv','TreatAsMissing','NA','SelectedVariableNames','ArrDelay','ReadSize',1000);

preview(ds)

meanDelay = mapreduce(ds,@meanArrivalDelayMapper,@meanArrivalDelayReducer,mr,...

            'OutputFolder',outputFolder);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

What's ' All the input files must be Sequence files. Invalid file: '' ' mean?

I have never seen it before. I just copy the code in the Matlab document.

I wish to know how to solve this problem. I have tried many methods to solve it.

Please give me some suggestions. Thanks.

[Rick Amos]

Duplicate of the answer:

http://www.mathworks.com/matlabcentral/answers/234017-how-to-solve-all-the-input-files-must-be-sequence-files-invalid-file