BLT file format

pyRCV2 accepts ballot data in the BLT file format, as described by Hill, Wichmann & Woodall for their implementation of Meek STV. The BLT file format is also used by OpenSTV/OpaVote, Lundell's Droop and Otten's eSTV (where it is known as a DAT data transfer file).

The file format is as follows:

4 2
3 1 3 4 0
4 1 3 2 0
2 4 1 3 0
1 2 0
2 2 4 3 1 0
1 3 4 2 0

The first line (4 2) indicates that there are 4 candidates for 2 vacancies. This must be on its own line.

The second line (-2), which is optional, indicates that the 2nd candidate (Basil) has withdrawn. Multiple withdrawn candidates may be specified on this line, e.g. -2 -3 -4. This must, if present, be on its own line.

The third line (second, if there are no withdrawn candidates) begins the ballot data. 3 1 3 4 0 indicates that there were 3 ballots which voted, in order of preference, for the 1st candidate (Adam), then the 3rd candidate (Charlotte), then the 4th candidate (Donald). A 0 optionally indicates the end of the list of preferences. Each such set of ballots must be on its own line.

The end of the list of ballots must be indicated with a single 0, which must be on its own line.

The next lines give the names of the candidates, up to the number of candidates specified on the first line (in this case, 4). Each candidate's name must be surrounded by quotation marks, and must appear on its own line.

The final line gives the name of the election, which must appear on its own line.

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