MATLAB: Big data question. how to generate a variable efficiently and aggregate

bigdata mapreduce tallarraysParallel Computing Toolbox

I have a file of tens of millions observations with a string identifier, which I load as a datastore:
  1. …………. V1 ….. V2 ………… V3 …….. V4
  2. # # * # KLM88 2001-06-30 10 COMPANY1
  3. # # * # KLM88 2000-12-31 20 COMPANY1
  4. # # * # MNH7C 2001-09-30 23 COMPANY1
  5. # # * # MNH7C 2001-06-30 15 COMPANY1
  6. # # * # MNH7C 2000-12-31 6 COMPANY1
  7. # # * # HG9LB 2000-12-31 2 COMPANY1
I also have a mat file with some extra information and matching of first variable:
  1. # KLM88 COUNTRYA
  2. # MNH7C COUNTRYA
  3. # HG9LB COUNTRYB
I wish for an end result such that I aggregate on country and date and company my dataset :
  1. # * # 2001-09-30 23 COMPANY1 COUNTRYA
  2. # * # 2001-06-30 25 COMPANY1 COUNTRYA
  3. # * # 2000-12-31 26 COMPANY1 COUNTRYA
  4. # * # HG9LB 2000-12-31 2 COMPANY1 COUNTRYB
I know I can do so by reading per dataChunk and with for loop assigning the country. However, that takes a huge amount of time. Any other suggestions of how to do so? I am fairly new to the concepts of tall arrays/ mapreduce etc. Thus, I am not sure how could I arrive to what I want more efficiently.
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