hedu表示父母教育水平，fedu为父亲学历，medu为母亲学历，当父母学历不同时，如何求出不同学历下不同家庭的个数？
clear
input str14 hhcode byte a02 float relation double(fedu medu) float(hedu cedu)
"1101010211201" 1 1 4 . 4 .
"1101010211201" 2 2 . 4 4 .
"1101010211201" 3 3 . . . 4
"1101010608501" 1 1 3 . 3 .
"1101010608501" 2 2 . 4 4 .
"1101010608501" 3 3 . . . 3
"1101011008801" 1 1 4 . 4 .
"1101011008801" 2 2 . 3 3 .
"1101011008801" 3 3 . . . 4
"1101011403701" 1 1 3 . 3 .
"1101011403701" 2 2 . 3 3 .
"1101011403701" 3 3 . . . 1
"1101011807001" 1 1 3 . 3 .
"1101011807001" 2 2 . 3 3 .
"1101011807001" 3 3 . . . 1
"1101011812201" 1 1 3 . 3 .
"1101011812201" 2 2 . 3 3 .
"1101011812201" 3 3 . . . 1
"1101012418901" 1 2 . 2 2 .
"1101012418901" 2 1 2 . 2 .
end
label values relation guanxii
label def guanxii 1 "father", modify
label def guanxii 2 "mother", modify
label def guanxii 3 "respondant", modify
label values fedu f
label values medu f
label def f 2 "junior middle", modify
label def f 3 "senior middle", modify
label def f 4 "undergraduate(more)", modify
label values cedu c
label def c 1 "elementary school", modify
label def c 3 "senior middle", modify
label def c 4 "undergraduate(more)", modify