读取一个文档
我需要defunction function然后输入一个洲的名字 ，然后会显示出这个洲所有的县城，如果输入不在这个文档的城市 显示 输入无效
具体要求（2. Using the datafile, write a FUNCTION named displayCounties which accepts one value representing the state name and then displays a list of all the counties for that state. Each county name should appear only once (I'd suggest when you find a county for the given state, only add it to your county list if it's not already in the list). The output should be nicely labeled (e.g. "The counties in Texas are followed by one county name per line). If the given state name is not found in the file your program should display "Invalid state was entered" and stop.）
文档格式是这样子 state是洲，county是县城
Year, State.county,state FIPs code,county FIPs
Code, Birth Rate
2003, Alabama, Autauga, 1, 1,48.4
2004, Alabama, Autauga, 1,1,46.4
2005, Alabama, Autauga, 1, 1, 44.1
2006, Alabama, Autauga, 1,1,44.3
2007,Alabama, Autauga, 1,1,43.7
2008, Alabama, Autauga,1,1,41.6
2009, Alabama, Autauga, 1,1, 38.7
2010, Alabama, Autauga, 1, 1, 34.7
2011, Alabama, Autauga, 1,1,31.9
2012, Alabama, Autauga, 1,1,30.3
2013, Alabama, Autauga, 1, 1,27.8
2014, Alabama, Autauga, 1, 1,26.1
2015, Alabama, Autauga, 1, 1, 24.7
2016, Alabama, Autauga, 1, 1, 23.3
2017, Alabama, Autauga, 1,1,22.4
2018, Alabama, Autauga, 1, 1, 21.5
2019, Alabama, Autauga, 1, 1,21.4
2020, Alabama, Autauga, 1, 1, 20.6
2003, Alabama, Baldwin,1,3,47.3
2004, Alabama, Baldwin, 1, 3,47.6
2005, Alabama, Baldwin, 1,3,47.6
2006, Alabama, Baldwin, 1, 3,50
2007, Alabama, Baldwin, 1,3,50.9
2008, Alabama, Baldwin, 1,3,49.4