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From Sebastian Neef <gehax...@mailbox.tu-berlin.de>
Subject Sequential/ordered map
Date Thu, 05 Jan 2017 10:51:48 GMT
Hello,

I'd like to implement an algorithm which doesn't really look
parallelizable to me, but maybe there's a way around it:

In general the algorithm looks like this:

1. Take a list of texts T_1 ... T_n
2. For every text T_i (i > 1) do
2.1: Split text into a list of words W_1 ... W_m
2.2: For every word W_j do:
2.2.1.: Check if word already existed in a prior text T_k ( i > k )
2.2.2.: If so, mark word W_j with k
2.2.3.: Else mark word W_j with i
3. Do something with texts based on marked words...

I have a DataSet<Text> with all texts T_1...T_n.

As far as I understand, I cannot simply .map(...) the DataSet, because
T_i's calculation is based on previous results (i.e. T_(i-1)).

My current solution would be to set the  parallelism to 1.

- Is there an elegant way to parallelize this algorithm?
- Does setting parallelism=1 guarantee a specific order of the DataSet?
- Is there a way to check if an element exists in a DataSet? E.g.
DataSet<>.contains(elem)?

Best regards,
Sebastian

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