Every operation with FirstNBuffer

[Uday]

Would like to understand the behavior of the FirstNBuffer operation used in conjunction with the Every operation.

For eg  

mainPipe = new GroupBy(mainPipe, groupByFields);

mainPipe = new Every(mainPipe, new FirstNBuffer(20), Fields.RESULTS);

say the pipe has a total of 100 records. If we apply a mean(average) calculation subsequently on the results of main pipe will it chain together 5 mean sets (20*5) & calculate 'mean of means' ?

Basically i'm trying to determine the effect of FirstNBuffer on a groupby for calculating mean/average type of operations. Because mean of means (on 5 sets) is not the same as mean on whole set (100 records).

Thanks for your inputs !