我有一个名为"sal"的数据框架，其中包含员工多年的工资信息。
我试图计算2013年只有一个人代表的职位数量。我知道，通过手动检查，答案是202。
我使用以下方法：
sal[sal['Year'] == 2013]['JobTitle'].nunique()
数据样本：
Id EmployeeName JobTitle BasePay OvertimePay OtherPay Benefits TotalPay TotalPayBenefits Year Notes Agency Status
72926 Gregory P Suhr Chief of Police 319275.01 0 20007.06 86533.21 339282.07 425815.28 2013 San Francisco
72927 Joanne M Hayes-White Chief, Fire Department 313686.01 0 23236 85431.39 336922.01 422353.4 2013 San Francisco
72928 Samson Lai Battalion Chief, Fire Suppress 186236.42 131217.63 29648.27 57064.95 347102.32 404167.27 2013 San Francisco
72929 Ellen G Moffatt Asst Med Examiner 272855.51 23727.91 38954.54 66198.92 335537.96 401736.88 2013 San Francisco
72930 Robert L Shaw Dep Dir for Investments, Ret 315572.01 0 0 82849.66 315572.01 398421.67 2013 San Francisco
72931 David L Franklin Asst Chf of Dept (Fire Dept) 215265.6 87985.24 30637.48 62890.36 333888.32 396778.68 2013 San Francisco
72932 Harlan L Kelly-Jr Executive Contract Employee 313312.52 0 0 82319.51 313312.52 395632.03 2013 San Francisco
72933 John L Martin Dept Head V 311758.96 0 1098.64 82476.85 312857.6 395334.45 2013 San Francisco
72934 Edward D Reiskin Gen Mgr, Public Trnsp Dept 305307.89 0 0 80860.6 305307.89 386168.49 2013 San Francisco
72935 Thomas A Siragusa Asst Chf of Dept (Fire Dept) 215265.6 88028.54 21526.49 61288.58 324820.63 386109.21 2013 San Francisco
72936 Amy P Hart Dept Head V 286480.44 0 17188.71 80077.63 303669.15 383746.78 2013 San Francisco
72937 Yifang Qian Senior Physician Specialist 203710 0 119176.84 58810.96 322886.84 381697.8 2013 San Francisco
72938 Michael J Biel Deputy Chief 3 278964 0 17587.86 77708.48 296551.86 374260.34 2013 San Francisco
72939 Raymond A Guzman Dep Chf of Dept (Fire Dept) 270756.03 0 24181.02 77474.92 294937.05 372411.97 2013 San Francisco
72940 Marty A Ross Battalion Chief, Fire Suppress 186236.43 88345.08 38035.09 58991.75 312616.6 371608.35 2013 San Francisco
72941 Mark A Gonzales Dep Chf of Dept (Fire Dept) 270756.01 0 20236.5 77408.16 290992.51 368400.67 2013 San Francisco
72942 Mark J Johnson Battalion Chief, Fire Suppress 186236.41 101466.96 23994.92 56134.3 311698.29 367832.59 2013 San Francisco
72943 Bryan W Rubenstein Battalion Chief, Fire Suppress 186236.45 94450.92 30313.49 56508.46 311000.86 367509.32 2013 San Francisco
72944 Gary L Altenberg Lieutenant, Fire Suppression 135903.02 163477.81 20994.96 46030.76 320375.79 366406.55 2013 San Francisco
72945 John J Loftus Deputy Chief 3 274126.5 0 13358.1 75909.1 287484.6 363393.7 2013 San Francisco
72946 Edwin M Lee Mayor 285446.37 0 0 77105.29 285446.37 362551.66 2013 San Francisco
72947 Michael J Morris Assistant Deputy Chief 2 124054 0 202322.37 35929.84 326376.37 362306.21 2013 San Francisco
72948 David Shinn Deputy Chief 3 278964 0 6428.79 76680.57 285392.79 362073.36 2013 San Francisco
72949 Arthur W Kenney Asst Chf of Dept (Fire Dept) 213308.64 49139.25 36262.42 60756.95 298710.31 359467.26 2013 San Francisco
72950 Lorrie A Kalos Battalion Chief, Fire Suppress 186236.49 87457.68 28003.53 57030.95 301697.7 358728.65 2013 San Francisco
72951 Lyn Tomioka Deputy Chief 3 278964 0 3536.35 76113.13 282500.35 358613.48 2013 San Francisco
72952 Denise A Schmitt Deputy Chief 3 278964 0 3536.39 75367.15 282500.39 357867.54 2013 San Francisco
72953 Rudy J Castellanos Battalion Chief, Fire Suppress 186236.42 94274.25 19022.95 55351.53 299533.62 354885.15 2013 San Francisco
72954 Susan Currin Adm, SFGH Medical Center 271831.5 0 5000 75511.72 276831.5 352343.22 2013 San Francisco
72955 Thomas F Abbott Battalion Chief, Fire Suppress 186236.41 84382.38 23279.44 56184.01 293898.23 350082.24 2013 San Francisco
72956 Naomi M Kelly Dept Head V 270641.5 0 3000 74867.87 273641.5 348509.37 2013 San Francisco
72957 Trent E Rhorer Dept Head V 270641.56 0 3000 74769.34 273641.56 348410.9 2013 San Francisco
72958 Barbara A Garcia Dept Head V 270591.04 0 3050.5 74769.33 273641.54 348410.87 2013 San Francisco
72959 Robert F Postel Asst Chf of Dept (Fire Dept) 212244.54 62490.6 13450.16 58778.57 288185.3 346963.87 2013 San Francisco
72960 Jeffrey J Barden Captain, Fire Suppression 155174.49 124293.83 18151.93 49001.55 297620.25 346621.8 2013 San Francisco
其正在返回1051的错误答案。有人能解释一下为什么我使用的逻辑是不正确的，以及另一种方法吗？
谢谢！！！
所以为了回答这个问题，我的逻辑错了：
sal[sal['Year'] == 2013]['JobTitle'].nunique()
将计算唯一职务的数量。因此，如果有10个人的职称是"工程师"，那就只算一次。
我想要的答案是"只有一个人代表的职位数量"；
我发现使用解决方案：
sum(sal[sal['Year']==2013]['JobTitle'].value_counts()==1)