如何在Lat-Long范围内找到变量的频率？

all.lat     all.long    all.season
41.69000    -71.56639   JJA
41.69000    -71.56639   MAM
41.69000    -72.56639   MAM
41.69000    -71.56639   MAM
41.69000    -71.56639   JJA
41.69000    -73.56639   MAM
41.69000    -71.56639   SON
41.69000    -73.56639   MAM
41.69000    -71.56639   JJA
41.69000    -74.56639   MAM
42.86250    -71.95972   DJF
42.86250    -75.95972   DJF
42.94806    -71.46389   JJA
42.94806    -71.46389   MAM
42.94806    -71.46389   MAM
42.84250    -71.70722   MAM
42.84250    -71.70722   JJA
42.94806    -75.46389   SON
42.94806    -75.46389   DJF
42.85750    -71.50667   MAM  
all.lat     all.long    all.season
41.69000