在R中将数据帧转换为data.table对象时，如何处理行名丢失的列？
为了在将R中的数据帧转换为data.table对象时处理缺少行名的列，我们在转换数据帧时需要使用keep.rownames参数。例如，如果我们有一个名为df的数据框，需要将其转换为一个data.table对象而又不丢失行名，则可以使用以下命令-
data.table(df,keep.rownames=TRUE)
示例
library(data.table) head(mtcars)输出结果
mpg cyl disp hp drat wt qsec vs am gear carb Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
示例
mtcars_data_table<-data.table(mtcars) mtcars_data_table输出结果
mpg cyl disp hp drat wt qsec vs am gear carb 1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4 2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4 3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 4: 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1 5: 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 6: 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 7: 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4 8: 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 9: 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 10: 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4 11: 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4 12: 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3 13: 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3 14: 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3 15: 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4 16: 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4 17: 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4 18: 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 19: 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 20: 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 21: 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 22: 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2 23: 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2 24: 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4 25: 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2 26: 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 27: 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2 28: 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 29: 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4 30: 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6 31: 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8 32: 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2 mpg cyl disp hp drat wt qsec vs am gear carb
上面的输出不包括汽车名称。如果我们想用汽车名称转换数据框，我们可以使用keep.rownames如下所示的参数-
示例
mtcars_data_table<-data.table(mtcars,keep.rownames=TRUE) mtcars_data_table输出结果
rn mpg cyl disp hp drat wt qsec vs am gear carb
1: Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4
2: Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4
3: Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1
4: Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1
5: Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2
6: Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1
7: Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4
8: Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2
9: Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2
10: Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4
11: Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4
12: Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3
13: Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3
14: Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3
15: Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4
16: Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4
17: Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4
18: Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1
19: Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2
20: Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1
21: Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1
22: Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2
23: AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.3 0 0 0 3 2
24: Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.410 0 3 4
25: Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2
26: Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1
27: Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2
28: Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2
29: Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4
30: Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6
31: Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8
32: Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
rn mpg cyl disp hp drat wt qsec vs am gear carb