Error (Reducer :) when trying to make a distinct reduction

Question

I get an error when I try to reduce the DISTINCT I got from here . I reproduced this error on a beer sample bucket, so it should be easy to reproduce. I did not see any errors in the mapreduce_errors.txt file or anything that could lead me to other places. (If you want me to search or send fragments of other files, please ask).

Launch of the 4th beta version of couchbase Enterprise on Windows 2008 R2 (this also happened in version 3.0.1.).

Here is my map function (using a beer sample bucket that comes directly with couchbase).

 function(doc, meta) { switch(doc.type) { case "brewery": emit(meta.id); break; } } 

Here is my reduction function:

 function(keys, values, rereduce) { return keys.filter(function (e, i, arr) { return arr.lastIndexOf(e) === i; }); } 

This is mistake:

reason: error (gear :)

Also imgur browsing pages if this helps: http://i.imgur.com/KyLutMc.png

Answer 1

The problem is your custom reduction function: you are not handling the case when it is called as part of a repeated reduction.

According to Couchbase Documentation :

The basic format of the reduce () function is as follows:

 function(key, values, rereduce) { ... return retval; } 

The reduction function has three arguments:

key : a key is a unique key obtained from the map () function and the group_level parameter.

values : The argument of values ​​is an array of all values ​​that match a particular key. For example, if the same key is displayed three times, the data will be an array of three elements containing, with each element containing the value output by the emit () function.

rereduce : Rereduce indicates whether the function is called as part of the reduction, that is, the called reduction function again to further reduce the input.

If rereduce false:

• The argument argument key will be an array, where the first argument is the key emitted by the map function, and id is the document identifier generated by the key.

• Values ​​are an array of values, where each element of the array corresponds to the corresponding element in the keys array.

If rereduce true:

• key will be null.

• values will be the array of values ​​returned by the previous reduce() function. The function should return the given version of the information by calling the return () function. The format of the return value must match the format required for the specified key.

Bold formatting belongs to me, and the highlighted words are very important: you should think that sometimes you get the keys argument with a null value.

According to the docs, you should handle the case where rereduce is true in your reduce() function, and you should know that in this case the keys will be null . In the case of your reduce() function, you can do something like this:

 function(keys, values, rereduce) { if (rereduce) { var result = []; for (var i = 0; i < values.length; i++) { var distinct = values[i]; for (var j = 0; j < distinct.length; j++) { result.push(distinct[j]); } } return result.filter(function (e, i, arr) { return arr.lastIndexOf(e) === i; }); } return keys.filter(function (e, i, arr) { return arr.lastIndexOf(e) === i; }); } 

Here I first process the phase of re-reduction. To do this, I smooth out the array of arrays that I get in the values argument, and then remove the duplicates that might appear after the merge.

Then comes the source code, which returns an array of keys arguments without duplicates.

To verify that this reduce() function really works, I used the following map() function:

 function(doc, meta) { switch(doc.type) { case "brewery": emit(meta.id, null); emit(meta.id, null); break; } } 

This intentionally creates duplicates, which are then removed by the reduce() function.

Answer 2

Although this reduction works as a development type, it is not a production type. The dataset must be too large, so you need to reuse it. This documentation should help http://docs.couchbase.com/admin/admin/Views/views-writing.html#reduce-functions