You can read the csv file in a private method like this http://groovy-almanac.org/csv-parser-with-groovy-categories/ and then you can assign the variables a and b like this:
where:
a << [readCSVAMap[0],readCSVAMap[1],readCSVAMap[2]]
b << [readCSVBMap[0],readCSVBMap[1],readCSVBMap[2]]