我有下表，我很想获得每个行业的lm斜坡数据框。每个行业的年份都是1999年 - 2012年，我只是在新表中寻找每个行业的斜率。
> head(mmfpdatad)
YEAR industry index
1 1999 Farms -0.02352551
2 2000 Farms 0.04081992
3 2001 Farms 0.02435490
4 2002 Farms 0.01056180
5 2003 Farms 0.04876939
6 2004 Farms -0.01805118
答案 0 :(得分：1)
使用mtcars作为示例数据，您可以尝试：
mtcars$slope <- ave(mtcars$mpg, as.factor(mtcars$gear), FUN = function(x) lm(x ~ seq_along(x))$coef[[2]])
给出了每档的坡度：
mtcars
mpg cyl disp hp drat wt qsec vs am gear carb slope
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4 0.6860140
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4 0.6860140
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 0.6860140
Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1 -0.1864286
Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 -0.1864286
Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 -0.1864286
Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4 -0.1864286
Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 0.6860140
Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 0.6860140
Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4 0.6860140
Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4 0.6860140
Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3 -0.1864286
Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3 -0.1864286
Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3 -0.1864286
Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4 -0.1864286
Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4 -0.1864286
Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4 -0.1864286
Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 0.6860140
Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 0.6860140
Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 0.6860140
Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 -0.1864286
Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2 -0.1864286
AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2 -0.1864286
Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4 -0.1864286
Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2 -0.1864286
Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 0.6860140
Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2 -3.2700000
Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 -3.2700000
Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4 -3.2700000
Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6 -3.2700000
Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8 -3.2700000
Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2 0.6860140