Weird MapReduce Behavior

Yehuda Zargrov Yehuda at
Tue Nov 29 04:26:32 EST 2011

Hi All,

We are facing a very strange map-reduce behavior.
We use ripple in ruby, this is the call:

  def yehuda
    query_result ='usage-test1')
     .map("function(v) { data = JSON.parse(v.values[0].data).loc; for (var a in data) { for (var b in data[a]) { for (var c in data[a][b]) { return [{date:v.key, sum:data[a][b][c]}]; } } } }")
     .reduce("function(v) {var s={}; for(var i in v)  { var date=''; var sum=0; for(var n in v[i]) { if (n === \"date\") date=v[i][n]; if (n === \"sum\") sum=v[i][n]; } if (date in s) s[date] += sum; else s[date] = sum; } return[v]; }", :keep => true).run

    puts query_result

The map function, though looks complicated, works fine. It gives the reduce an array of hashes like this:
{"date"=>"CT16-20110114", "sum"=>1}
{"date"=>"CT18-20101204", "sum"=>1}
{"date"=>"CT19-20110314", "sum"=>1}
{"date"=>"CT116-20100516", "sum"=>1}
{"date"=>"CT17-20110214", "sum"=>1}
{"date"=>"CT19-20100511", "sum"=>1}
{"date"=>"CT18-20100710", "sum"=>1}
{"date"=>"CT19-20110301", "sum"=>1}
{"date"=>"CT17-20110213", "sum"=>1}

There are a lot of items in this array (hundreds).
The reduce function should sum up the total sum of every date.
>From some reason it returns only 13 results:
{""=>0, "CT18-20101222"=>1, "CT116-20101123"=>1, "CT18-20101208"=>1, "CT18-20101110"=>1, "CT116-20101028"=>1, "CT18-20100904"=>1, "CT18-20100820"=>1, "CT18-20100618"=>1, "CT17-20110420"=>1, "CT17-20110412"=>1, "CT17-20110407"=>1, "CT17-20110401"=>1}.

Does someone have a clue why?


Yehuda Zargarov

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Yehuda Zargrov
Software Engineer
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