Is the tab the delimiter between records or between keys and values on the
input?
in other words does the input file look like this:
a\tb
b\tc
c\ta
or does it look like this:
a b\tb c\tc a\t
?
Jeff
On Thu, Jul 15, 2010 at 6:18 PM, Nikolay Korovaiko <korovai...@gmail.com>wrote:
> Hi everyone,
>
> I hope this is the right place for my question. If not, please, feel free
> to
> ignore it ;) and I'm sorry for any inconvenience made :(
>
> I'm writing a simple program for enumerating triangles in directed graphs
> for my project. First, for each input arc (e.g. a b, b c, c a, note: a tab
> symbol serves as a delimiter) I want my map function output the following
> pairs ([a, to_b], [b, from_a], [a_b, -1]):
>
> public void map(LongWritable key, Text value,
>
> OutputCollector<Text, Text> output,
>
> Reporter reporter) throws IOException {
>
> String line = value.toString();
>
> String [] tokens = line.split(" ");
>
> output.collect(new Text(tokens[0]), new Text("to_"+tokens[1]));
>
> output.collect(new Text(tokens[1]), new Text("from_"+tokens[0]));
>
> output.collect(new Text(tokens[0]+"_"+tokens[1]), new Text("-1"));
>
> }
>
> Now my reduce function is supposed to cross join all pairs that have both
> to_'s and from_'s and to simply propogate any other pairs whose keys
> contain
> "_".
>
> public void reduce(Text key, Iterator<Text> values,
>
> OutputCollector<Text, Text> output,
>
> Reporter reporter) throws IOException {
>
> String key_s = key.toString();
>
> if (key_s.indexOf("_")>0)
>
> output.collect(key, new Text("completed"));
>
> else {
>
> HashMap <String, ArrayList<String>> lists = new HashMap
> <String, ArrayList<String>> ();
>
> while (values.hasNext()) {
>
> String line = values.next().toString();
>
> String[] tokens = line.split("_");
>
> if (!lists.containsKey(tokens[0])) {
>
> lists.put(tokens[0], new ArrayList<String>());
>
> }
> lists.get(tokens[0]).add(tokens[1]);
>
> }
>
> for (String t : lists.get("to"))
>
> for (String f : lists.get("from"))
>
> output.collect(new Text(t+"_"+f), key);
>
>
> }
>
> }
>
> And this is where the most exciting stuff happens. tokens[1] yields an
> ArrayOutOfBounds exception. If you scroll up, you can see that by this
> point
> the iterator should give values like "to_a", "from_b", "to_b", etc... when
> I
> just output these values, everything looks ok and I have "to_a", "from_b".
> But split() don't work at all, moreover line.length() is always 1 and
> indexOf("*") returns -1! The very same indexOf WORKS PERFECTLY for keys...
> where we have pairs whose keys contain "_"* and look like "a_b", "b_c"
>
> I'm really puzzled with all this. MapReduce is supposed to save lives
> making
> everything simple. Instead I spent several hours to just spot this...
>
> I'd really appreciate your help, guys!!! Thanks in advance!
>
