我想知道如何将嵌套的 for 循环替换为 R 编程中更简洁的形式。
我的变量名是：
names(Auto[-1])
“气缸”“排量”“马力”“重量”“加速度”“年份”“产地”
所以我做了一个简单的 for 循环：
for (var1 in names(Auto[-1]))
{
listanova[var] = summary(lm((paste('mpg ~',var1)), data = Auto))[6]$sigma
}
我怎样才能做一个更复杂的 for 循环而不是嵌套，我想避免长而复杂的 for 循环。例如，我想迭代 var1*var2+var3 的所有可能性，其中这些变量是 Auto[-1] 的变量。有可能吗？
【问题讨论】：
我认为mpg ~ Var1 * Var2 + Var3 需要combn 2 个变量与expand.grid 的组合，而不仅仅是combn 3，因为Var1 * Var2 == Var2 * Var1，而是Var1 * Var2 + Var3！ = Var1 * Var3 + Var2.
这是解决此问题的一种方法：
library(ISLR)
data(Auto)
cols <- names(Auto)[-1]
res <- expand.grid(combn(cols, 2, simplify=FALSE), cols)
res <- res[lengths(apply(res, 1,
function(x) intersect(as.character(x$Var2), unlist(x$Var1)))) == 0,]
res <- setNames(data.frame(
t(data.frame(res$Var1)), as.character(res$Var2), row.names = NULL),
paste0("Var", 1:3))
res$sigma <- apply(res, 1,
function(x) sigma(lm(paste0("mpg ~ ", x[1], " * ", x[2], " + ", x[3]),
data = Auto)))
res
#> Var1 Var2 Var3 sigma
#> 1 displacement horsepower cylinders 3.930608
#> 2 displacement weight cylinders 4.101442
#> 3 displacement acceleration cylinders 4.461698
#> 4 displacement year cylinders 3.733483
#> 5 displacement origin cylinders 4.520063
#> 6 displacement name cylinders 2.422872
#> 7 horsepower weight cylinders 3.931893
#> 8 horsepower acceleration cylinders 4.229184
#> 9 horsepower year cylinders 3.650538
#> 10 horsepower origin cylinders 4.169378
#> 11 horsepower name cylinders 2.558382
#> 12 weight acceleration cylinders 4.230993
#> 13 weight year cylinders 3.195613
#> 14 weight origin cylinders 4.209175
#> 15 weight name cylinders 2.575035
#> 16 acceleration year cylinders 4.108109
#> 17 acceleration origin cylinders 4.623440
#> 18 acceleration name cylinders 2.752275
#> 19 year origin cylinders 3.957220
#> 20 year name cylinders 2.373485
#> 21 origin name cylinders 2.852769
#> 22 cylinders horsepower displacement 3.996131
#> 23 cylinders weight displacement 4.144523
#> 24 cylinders acceleration displacement 4.546081
#> 25 cylinders year displacement 3.820275
#> 26 cylinders origin displacement 4.586554
#> 27 cylinders name displacement 2.824717
#> 28 horsepower weight displacement 3.927991
#> 29 horsepower acceleration displacement 4.098049
#> 30 horsepower year displacement 3.511056
#> 31 horsepower origin displacement 4.130212
#> 32 horsepower name displacement 2.435430
#> 33 weight acceleration displacement 4.210034
#> 34 weight year displacement 3.192645
#> 35 weight origin displacement 4.199256
#> 36 weight name displacement 2.624553
#> 37 acceleration year displacement 3.767955
#> 38 acceleration origin displacement 4.391746
#> 39 acceleration name displacement 2.763000
#> 40 year origin displacement 3.828119
#> 41 year name displacement 2.211958
#> 42 origin name displacement 2.776667
#> 43 cylinders displacement horsepower 4.150379
#> 44 cylinders weight horsepower 4.003118
#> 45 cylinders acceleration horsepower 4.361433
#> 46 cylinders year horsepower 3.858321
#> 47 cylinders origin horsepower 4.411365
#> 48 cylinders name horsepower 2.794140
#> 49 displacement weight horsepower 3.952595
#> 50 displacement acceleration horsepower 4.144063
#> 51 displacement year horsepower 3.625651
#> 52 displacement origin horsepower 4.391267
#> 53 displacement name horsepower 2.437027
#> 54 weight acceleration horsepower 4.141952
#> 55 weight year horsepower 3.160076
#> 56 weight origin horsepower 4.126864
#> 57 weight name horsepower 2.600191
#> 58 acceleration year horsepower 4.048410
#> 59 acceleration origin horsepower 4.322450
#> 60 acceleration name horsepower 2.542587
#> 61 year origin horsepower 3.956825
#> 62 year name horsepower 2.256631
#> 63 origin name horsepower 2.797134
#> 64 cylinders displacement weight 4.192360
#> 65 cylinders horsepower weight 3.897318
#> 66 cylinders acceleration weight 4.267501
#> 67 cylinders year weight 3.288582
#> 68 cylinders origin weight 4.253179
#> 69 cylinders name weight 2.801128
#> 70 displacement horsepower weight 3.875941
#> 71 displacement acceleration weight 4.216553
#> 72 displacement year weight 3.247050
#> 73 displacement origin weight 4.248519
#> 74 displacement name weight 2.410626
#> 75 horsepower acceleration weight 4.120773
#> 76 horsepower year weight 3.111929
#> 77 horsepower origin weight 3.994020
#> 78 horsepower name weight 2.491070
#> 79 acceleration year weight 3.282754
#> 80 acceleration origin weight 4.153596
#> 81 acceleration name weight 2.782508
#> 82 year origin weight 3.298971
#> 83 year name weight 1.842066
#> 84 origin name weight 2.766529
#> 85 cylinders displacement acceleration 4.451150
#> 86 cylinders horsepower acceleration 3.964971
#> 87 cylinders weight acceleration 4.100272
#> 88 cylinders year acceleration 4.135679
#> 89 cylinders origin acceleration 4.761837
#> 90 cylinders name acceleration 2.890067
#> 91 displacement horsepower acceleration 3.848881
#> 92 displacement weight acceleration 4.056102
#> 93 displacement year acceleration 3.732550
#> 94 displacement origin acceleration 4.530853
#> 95 displacement name acceleration 2.205730
#> 96 horsepower weight acceleration 3.923677
#> 97 horsepower year acceleration 3.705777
#> 98 horsepower origin acceleration 4.282692
#> 99 horsepower name acceleration 2.322535
#> 100 weight year acceleration 3.156020
#> 101 weight origin acceleration 4.200064
#> 102 weight name acceleration 2.633103
#> 103 year origin acceleration 5.008915
#> 104 year name acceleration 2.494472
#> 105 origin name acceleration 2.942866
#> 106 cylinders displacement year 3.628036
#> 107 cylinders horsepower year 3.375560
#> 108 cylinders weight year 3.092482
#> 109 cylinders acceleration year 4.078887
#> 110 cylinders origin year 4.005163
#> 111 cylinders name year 2.640081
#> 112 displacement horsepower year 3.169038
#> 113 displacement weight year 3.019469
#> 114 displacement acceleration year 3.569871
#> 115 displacement origin year 3.743455
#> 116 displacement name year 2.327629
#> 117 horsepower weight year 2.963053
#> 118 horsepower acceleration year 3.725775
#> 119 horsepower origin year 3.819683
#> 120 horsepower name year 2.432993
#> 121 weight acceleration year 3.223483
#> 122 weight origin year 3.263234
#> 123 weight name year 1.926429
#> 124 acceleration origin year 4.978284
#> 125 acceleration name year 2.719680
#> 126 origin name year 2.659251
#> 127 cylinders displacement origin 4.454612
#> 128 cylinders horsepower origin 3.992428
#> 129 cylinders weight origin 4.151961
#> 130 cylinders acceleration origin 4.759292
#> 131 cylinders year origin 3.950697
#> 132 cylinders name origin 2.880736
#> 133 displacement horsepower origin 3.916857
#> 134 displacement weight origin 4.099032
#> 135 displacement acceleration origin 4.444354
#> 136 displacement year origin 3.679281
#> 137 displacement name origin 2.419996
#> 138 horsepower weight origin 3.889403
#> 139 horsepower acceleration origin 4.197468
#> 140 horsepower year origin 3.560784
#> 141 horsepower name origin 2.547681
#> 142 weight acceleration origin 4.194124
#> 143 weight year origin 3.140978
#> 144 weight name origin 2.611288
#> 145 acceleration year origin 5.012415
#> 146 acceleration name origin 2.956412
#> 147 year name origin 2.473915
#> 148 cylinders displacement name 2.733227
#> 149 cylinders horsepower name 2.652409
#> 150 cylinders weight name 2.717629
#> 151 cylinders acceleration name 2.869345
#> 152 cylinders year name 2.580032
#> 153 cylinders origin name 2.852769
#> 154 displacement horsepower name 2.628840
#> 155 displacement weight name 2.698532
#> 156 displacement acceleration name 2.708595
#> 157 displacement year name 2.406705
#> 158 displacement origin name 2.719861
#> 159 horsepower weight name 2.648480
#> 160 horsepower acceleration name 2.555832
#> 161 horsepower year name 2.453807
#> 162 horsepower origin name 2.682554
#> 163 weight acceleration name 2.797606
#> 164 weight year name 2.294686
#> 165 weight origin name 2.738440
#> 166 acceleration year name 2.662019
#> 167 acceleration origin name 2.899071
#> 168 year origin name 2.630942
由reprex package (v0.3.0) 于 2020 年 6 月 14 日创建
【讨论】：
reprex 包制作的，它应该使其可重现而无需任何额外的依赖。您是否在复制示例时遇到问题，或者您自己的数据有问题？