cylinders displacement horsepower weight acceleration model origin class
1 8 307.0 130 3504 12.0 70 1 18.0
2 8 350.0 165 3693 11.5 70 1 15.0
3 8 318.0 150 3436 11.0 70 1 18.0
4 8 304.0 150 3433 12.0 70 1 16.0
5 8 302.0 140 3449 10.5 70 1 17.0
6 8 429.0 198 4341 10.0 70 1 15.0
7 8 454.0 220 4354 9.0 70 1 14.0
8 8 440.0 215 4312 8.5 70 1 14.0
9 8 455.0 225 4425 10.0 70 1 14.0
10 8 390.0 190 3850 8.5 70 1 15.0
11 8 383.0 170 3563 10.0 70 1 15.0
12 8 340.0 160 3609 8.0 70 1 14.0
13 8 400.0 150 3761 9.5 70 1 15.0
14 8 455.0 225 3086 10.0 70 1 14.0
15 4 113.0 95 2372 15.0 70 3 24.0
16 6 198.0 95 2833 15.5 70 1 22.0
17 6 199.0 97 2774 15.5 70 1 18.0
18 6 200.0 85 2587 16.0 70 1 21.0
19 4 97.0 88 2130 14.5 70 3 27.0
20 4 97.0 46 1835 20.5 70 2 26.0
21 4 110.0 87 2672 17.5 70 2 25.0
22 4 107.0 90 2430 14.5 70 2 24.0
23 4 104.0 95 2375 17.5 70 2 25.0
假设上面是我的数据框，我如何计算其原点为2的行号？即应该是4
答案 0 :(得分：2)
nrow(df[df$origin == 2,])
# or slightly quicker
length(df[df$origin == 2, 1]) # subset will be marginally quicker
或者@akrun就在上面。