起因
碰到一个同学有如此问题:
within(mtcars,{
cyl[cyl<=4] <- "hello"
cyl[cyl>=8] <- "world"
cyl[cyl>4 & cyl<8] <- "!"
})
#> mpg cyl disp hp drat wt qsec vs am gear carb
#> Mazda RX4 21.0 ! 160.0 110 3.90 2.620 16.46 0 1 4 4
#> Mazda RX4 Wag 21.0 ! 160.0 110 3.90 2.875 17.02 0 1 4 4
#> Datsun 710 22.8 world 108.0 93 3.85 2.320 18.61 1 1 4 1
#> Hornet 4 Drive 21.4 ! 258.0 110 3.08 3.215 19.44 1 0 3 1
#> Hornet Sportabout 18.7 world 360.0 175 3.15 3.440 17.02 0 0 3 2
#> Valiant 18.1 ! 225.0 105 2.76 3.460 20.22 1 0 3 1
#> Duster 360 14.3 world 360.0 245 3.21 3.570 15.84 0 0 3 4
#> Merc 240D 24.4 world 146.7 62 3.69 3.190 20.00 1 0 4 2
#> Merc 230 22.8 world 140.8 95 3.92 3.150 22.90 1 0 4 2
#> Merc 280 19.2 ! 167.6 123 3.92 3.440 18.30 1 0 4 4
#> Merc 280C 17.8 ! 167.6 123 3.92 3.440 18.90 1 0 4 4
#> Merc 450SE 16.4 world 275.8 180 3.07 4.070 17.40 0 0 3 3
#> Merc 450SL 17.3 world 275.8 180 3.07 3.730 17.60 0 0 3 3
#> Merc 450SLC 15.2 world 275.8 180 3.07 3.780 18.00 0 0 3 3
#> Cadillac Fleetwood 10.4 world 472.0 205 2.93 5.250 17.98 0 0 3 4
#> Lincoln Continental 10.4 world 460.0 215 3.00 5.424 17.82 0 0 3 4
#> Chrysler Imperial 14.7 world 440.0 230 3.23 5.345 17.42 0 0 3 4
#> Fiat 128 32.4 world 78.7 66 4.08 2.200 19.47 1 1 4 1
#> Honda Civic 30.4 world 75.7 52 4.93 1.615 18.52 1 1 4 2
#> Toyota Corolla 33.9 world 71.1 65 4.22 1.835 19.90 1 1 4 1
#> Toyota Corona 21.5 world 120.1 97 3.70 2.465 20.01 1 0 3 1
#> Dodge Challenger 15.5 world 318.0 150 2.76 3.520 16.87 0 0 3 2
#> AMC Javelin 15.2 world 304.0 150 3.15 3.435 17.30 0 0 3 2
#> Camaro Z28 13.3 world 350.0 245 3.73 3.840 15.41 0 0 3 4
#> Pontiac Firebird 19.2 world 400.0 175 3.08 3.845 17.05 0 0 3 2
#> Fiat X1-9 27.3 world 79.0 66 4.08 1.935 18.90 1 1 4 1
#> Porsche 914-2 26.0 world 120.3 91 4.43 2.140 16.70 0 1 5 2
#> Lotus Europa 30.4 world 95.1 113 3.77 1.513 16.90 1 1 5 2
#> Ford Pantera L 15.8 world 351.0 264 4.22 3.170 14.50 0 1 5 4
#> Ferrari Dino 19.7 ! 145.0 175 3.62 2.770 15.50 0 1 5 6
#> Maserati Bora 15.0 world 301.0 335 3.54 3.570 14.60 0 1 5 8
#> Volvo 142E 21.4 world 121.0 109 4.11 2.780 18.60 1 1 4 2
<sup>Created on 2019-04-02 by the reprex package (v0.2.1)</sup>
发现预期与结果不一样。
自己又尝试了以下结果竟然是这样:
"hello">=8
#> [1] TRUE
"">=8
#> [1] FALSE
'k'>=8000000
#> [1] TRUE
<sup>Created on 2019-04-02 by the reprex package (v0.2.1)</sup>
困惑
- 为什么非空字符大于数字?
- 在1的条件下,
cyl[cyl>4 & cyl<8] <- "!"
竟然判别出了那个6,这又是什么原因?