NOTES ON THE BASE FILES
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The base files contain transaction-level data and are separated by year. The naming convention for the files is "base_file_yyyy.csv." NOTE, the individual files are quite large, so it is recommended that you avoid appending all files unless you are working on a computer that can handle it. It is more efficient to, instead, loop over individual files and aggregate before appending. 


The variables included in each file are: 

++ year:  the calendar year that the transaction took place

++ action_date: the date that the transaction took place

++ contract_transaction_unique_key: a unique identifier for the transaction 

++ contract_award_unqiue_key: a unique identifier for the award that the transaction is a part of

++ modification_number: a code associated with transactions that are modifications of established awards

++ awarding_agency_code: a code number for the agency awarding the contract. A separate crosswalk providing the agency name for each associated code is contained in "crosswalk_awarding_agency.csv"

++ recipient_duns: an identifying code for the contract recipient

++ recipient_name: the name of the recipient firm 

++ naics_code: the six-digit NAICS code of the industry that the contract is relevant for

++ period_of_performance_start_date: the transaction's start date

++ period_of_performance_current_end_date: the transaction's expected end date

++ federal_action_obligation: federal dollars obligated for the given transaction