library(MASS)
dat <- MASS::birthwt
(dat)
##     low age lwt race smoke ptl ht ui ftv  bwt
## 85    0  19 182    2     0   0  0  1   0 2523
## 86    0  33 155    3     0   0  0  0   3 2551
## 87    0  20 105    1     1   0  0  0   1 2557
## 88    0  21 108    1     1   0  0  1   2 2594
## 89    0  18 107    1     1   0  0  1   0 2600
## 91    0  21 124    3     0   0  0  0   0 2622
## 92    0  22 118    1     0   0  0  0   1 2637
## 93    0  17 103    3     0   0  0  0   1 2637
## 94    0  29 123    1     1   0  0  0   1 2663
## 95    0  26 113    1     1   0  0  0   0 2665
## 96    0  19  95    3     0   0  0  0   0 2722
## 97    0  19 150    3     0   0  0  0   1 2733
## 98    0  22  95    3     0   0  1  0   0 2751
## 99    0  30 107    3     0   1  0  1   2 2750
## 100   0  18 100    1     1   0  0  0   0 2769
## 101   0  18 100    1     1   0  0  0   0 2769
## 102   0  15  98    2     0   0  0  0   0 2778
## 103   0  25 118    1     1   0  0  0   3 2782
## 104   0  20 120    3     0   0  0  1   0 2807
## 105   0  28 120    1     1   0  0  0   1 2821
## 106   0  32 121    3     0   0  0  0   2 2835
## 107   0  31 100    1     0   0  0  1   3 2835
## 108   0  36 202    1     0   0  0  0   1 2836
## 109   0  28 120    3     0   0  0  0   0 2863
## 111   0  25 120    3     0   0  0  1   2 2877
## 112   0  28 167    1     0   0  0  0   0 2877
## 113   0  17 122    1     1   0  0  0   0 2906
## 114   0  29 150    1     0   0  0  0   2 2920
## 115   0  26 168    2     1   0  0  0   0 2920
## 116   0  17 113    2     0   0  0  0   1 2920
## 117   0  17 113    2     0   0  0  0   1 2920
## 118   0  24  90    1     1   1  0  0   1 2948
## 119   0  35 121    2     1   1  0  0   1 2948
## 120   0  25 155    1     0   0  0  0   1 2977
## 121   0  25 125    2     0   0  0  0   0 2977
## 123   0  29 140    1     1   0  0  0   2 2977
## 124   0  19 138    1     1   0  0  0   2 2977
## 125   0  27 124    1     1   0  0  0   0 2922
## 126   0  31 215    1     1   0  0  0   2 3005
## 127   0  33 109    1     1   0  0  0   1 3033
## 128   0  21 185    2     1   0  0  0   2 3042
## 129   0  19 189    1     0   0  0  0   2 3062
## 130   0  23 130    2     0   0  0  0   1 3062
## 131   0  21 160    1     0   0  0  0   0 3062
## 132   0  18  90    1     1   0  0  1   0 3062
## 133   0  18  90    1     1   0  0  1   0 3062
## 134   0  32 132    1     0   0  0  0   4 3080
## 135   0  19 132    3     0   0  0  0   0 3090
## 136   0  24 115    1     0   0  0  0   2 3090
## 137   0  22  85    3     1   0  0  0   0 3090
## 138   0  22 120    1     0   0  1  0   1 3100
## 139   0  23 128    3     0   0  0  0   0 3104
## 140   0  22 130    1     1   0  0  0   0 3132
## 141   0  30  95    1     1   0  0  0   2 3147
## 142   0  19 115    3     0   0  0  0   0 3175
## 143   0  16 110    3     0   0  0  0   0 3175
## 144   0  21 110    3     1   0  0  1   0 3203
## 145   0  30 153    3     0   0  0  0   0 3203
## 146   0  20 103    3     0   0  0  0   0 3203
## 147   0  17 119    3     0   0  0  0   0 3225
## 148   0  17 119    3     0   0  0  0   0 3225
## 149   0  23 119    3     0   0  0  0   2 3232
## 150   0  24 110    3     0   0  0  0   0 3232
## 151   0  28 140    1     0   0  0  0   0 3234
## 154   0  26 133    3     1   2  0  0   0 3260
## 155   0  20 169    3     0   1  0  1   1 3274
## 156   0  24 115    3     0   0  0  0   2 3274
## 159   0  28 250    3     1   0  0  0   6 3303
## 160   0  20 141    1     0   2  0  1   1 3317
## 161   0  22 158    2     0   1  0  0   2 3317
## 162   0  22 112    1     1   2  0  0   0 3317
## 163   0  31 150    3     1   0  0  0   2 3321
## 164   0  23 115    3     1   0  0  0   1 3331
## 166   0  16 112    2     0   0  0  0   0 3374
## 167   0  16 135    1     1   0  0  0   0 3374
## 168   0  18 229    2     0   0  0  0   0 3402
## 169   0  25 140    1     0   0  0  0   1 3416
## 170   0  32 134    1     1   1  0  0   4 3430
## 172   0  20 121    2     1   0  0  0   0 3444
## 173   0  23 190    1     0   0  0  0   0 3459
## 174   0  22 131    1     0   0  0  0   1 3460
## 175   0  32 170    1     0   0  0  0   0 3473
## 176   0  30 110    3     0   0  0  0   0 3544
## 177   0  20 127    3     0   0  0  0   0 3487
## 179   0  23 123    3     0   0  0  0   0 3544
## 180   0  17 120    3     1   0  0  0   0 3572
## 181   0  19 105    3     0   0  0  0   0 3572
## 182   0  23 130    1     0   0  0  0   0 3586
## 183   0  36 175    1     0   0  0  0   0 3600
## 184   0  22 125    1     0   0  0  0   1 3614
## 185   0  24 133    1     0   0  0  0   0 3614
## 186   0  21 134    3     0   0  0  0   2 3629
## 187   0  19 235    1     1   0  1  0   0 3629
## 188   0  25  95    1     1   3  0  1   0 3637
## 189   0  16 135    1     1   0  0  0   0 3643
## 190   0  29 135    1     0   0  0  0   1 3651
## 191   0  29 154    1     0   0  0  0   1 3651
## 192   0  19 147    1     1   0  0  0   0 3651
## 193   0  19 147    1     1   0  0  0   0 3651
## 195   0  30 137    1     0   0  0  0   1 3699
## 196   0  24 110    1     0   0  0  0   1 3728
## 197   0  19 184    1     1   0  1  0   0 3756
## 199   0  24 110    3     0   1  0  0   0 3770
## 200   0  23 110    1     0   0  0  0   1 3770
## 201   0  20 120    3     0   0  0  0   0 3770
## 202   0  25 241    2     0   0  1  0   0 3790
## 203   0  30 112    1     0   0  0  0   1 3799
## 204   0  22 169    1     0   0  0  0   0 3827
## 205   0  18 120    1     1   0  0  0   2 3856
## 206   0  16 170    2     0   0  0  0   4 3860
## 207   0  32 186    1     0   0  0  0   2 3860
## 208   0  18 120    3     0   0  0  0   1 3884
## 209   0  29 130    1     1   0  0  0   2 3884
## 210   0  33 117    1     0   0  0  1   1 3912
## 211   0  20 170    1     1   0  0  0   0 3940
## 212   0  28 134    3     0   0  0  0   1 3941
## 213   0  14 135    1     0   0  0  0   0 3941
## 214   0  28 130    3     0   0  0  0   0 3969
## 215   0  25 120    1     0   0  0  0   2 3983
## 216   0  16  95    3     0   0  0  0   1 3997
## 217   0  20 158    1     0   0  0  0   1 3997
## 218   0  26 160    3     0   0  0  0   0 4054
## 219   0  21 115    1     0   0  0  0   1 4054
## 220   0  22 129    1     0   0  0  0   0 4111
## 221   0  25 130    1     0   0  0  0   2 4153
## 222   0  31 120    1     0   0  0  0   2 4167
## 223   0  35 170    1     0   1  0  0   1 4174
## 224   0  19 120    1     1   0  0  0   0 4238
## 225   0  24 116    1     0   0  0  0   1 4593
## 226   0  45 123    1     0   0  0  0   1 4990
## 4     1  28 120    3     1   1  0  1   0  709
## 10    1  29 130    1     0   0  0  1   2 1021
## 11    1  34 187    2     1   0  1  0   0 1135
## 13    1  25 105    3     0   1  1  0   0 1330
## 15    1  25  85    3     0   0  0  1   0 1474
## 16    1  27 150    3     0   0  0  0   0 1588
## 17    1  23  97    3     0   0  0  1   1 1588
## 18    1  24 128    2     0   1  0  0   1 1701
## 19    1  24 132    3     0   0  1  0   0 1729
## 20    1  21 165    1     1   0  1  0   1 1790
## 22    1  32 105    1     1   0  0  0   0 1818
## 23    1  19  91    1     1   2  0  1   0 1885
## 24    1  25 115    3     0   0  0  0   0 1893
## 25    1  16 130    3     0   0  0  0   1 1899
## 26    1  25  92    1     1   0  0  0   0 1928
## 27    1  20 150    1     1   0  0  0   2 1928
## 28    1  21 200    2     0   0  0  1   2 1928
## 29    1  24 155    1     1   1  0  0   0 1936
## 30    1  21 103    3     0   0  0  0   0 1970
## 31    1  20 125    3     0   0  0  1   0 2055
## 32    1  25  89    3     0   2  0  0   1 2055
## 33    1  19 102    1     0   0  0  0   2 2082
## 34    1  19 112    1     1   0  0  1   0 2084
## 35    1  26 117    1     1   1  0  0   0 2084
## 36    1  24 138    1     0   0  0  0   0 2100
## 37    1  17 130    3     1   1  0  1   0 2125
## 40    1  20 120    2     1   0  0  0   3 2126
## 42    1  22 130    1     1   1  0  1   1 2187
## 43    1  27 130    2     0   0  0  1   0 2187
## 44    1  20  80    3     1   0  0  1   0 2211
## 45    1  17 110    1     1   0  0  0   0 2225
## 46    1  25 105    3     0   1  0  0   1 2240
## 47    1  20 109    3     0   0  0  0   0 2240
## 49    1  18 148    3     0   0  0  0   0 2282
## 50    1  18 110    2     1   1  0  0   0 2296
## 51    1  20 121    1     1   1  0  1   0 2296
## 52    1  21 100    3     0   1  0  0   4 2301
## 54    1  26  96    3     0   0  0  0   0 2325
## 56    1  31 102    1     1   1  0  0   1 2353
## 57    1  15 110    1     0   0  0  0   0 2353
## 59    1  23 187    2     1   0  0  0   1 2367
## 60    1  20 122    2     1   0  0  0   0 2381
## 61    1  24 105    2     1   0  0  0   0 2381
## 62    1  15 115    3     0   0  0  1   0 2381
## 63    1  23 120    3     0   0  0  0   0 2410
## 65    1  30 142    1     1   1  0  0   0 2410
## 67    1  22 130    1     1   0  0  0   1 2410
## 68    1  17 120    1     1   0  0  0   3 2414
## 69    1  23 110    1     1   1  0  0   0 2424
## 71    1  17 120    2     0   0  0  0   2 2438
## 75    1  26 154    3     0   1  1  0   1 2442
## 76    1  20 105    3     0   0  0  0   3 2450
## 77    1  26 190    1     1   0  0  0   0 2466
## 78    1  14 101    3     1   1  0  0   0 2466
## 79    1  28  95    1     1   0  0  0   2 2466
## 81    1  14 100    3     0   0  0  0   2 2495
## 82    1  23  94    3     1   0  0  0   0 2495
## 83    1  17 142    2     0   0  1  0   0 2495
## 84    1  21 130    1     1   0  1  0   3 2495
dat$race <- c("White", "Black", "Other")[dat$race]
(dat)
##     low age lwt  race smoke ptl ht ui ftv  bwt
## 85    0  19 182 Black     0   0  0  1   0 2523
## 86    0  33 155 Other     0   0  0  0   3 2551
## 87    0  20 105 White     1   0  0  0   1 2557
## 88    0  21 108 White     1   0  0  1   2 2594
## 89    0  18 107 White     1   0  0  1   0 2600
## 91    0  21 124 Other     0   0  0  0   0 2622
## 92    0  22 118 White     0   0  0  0   1 2637
## 93    0  17 103 Other     0   0  0  0   1 2637
## 94    0  29 123 White     1   0  0  0   1 2663
## 95    0  26 113 White     1   0  0  0   0 2665
## 96    0  19  95 Other     0   0  0  0   0 2722
## 97    0  19 150 Other     0   0  0  0   1 2733
## 98    0  22  95 Other     0   0  1  0   0 2751
## 99    0  30 107 Other     0   1  0  1   2 2750
## 100   0  18 100 White     1   0  0  0   0 2769
## 101   0  18 100 White     1   0  0  0   0 2769
## 102   0  15  98 Black     0   0  0  0   0 2778
## 103   0  25 118 White     1   0  0  0   3 2782
## 104   0  20 120 Other     0   0  0  1   0 2807
## 105   0  28 120 White     1   0  0  0   1 2821
## 106   0  32 121 Other     0   0  0  0   2 2835
## 107   0  31 100 White     0   0  0  1   3 2835
## 108   0  36 202 White     0   0  0  0   1 2836
## 109   0  28 120 Other     0   0  0  0   0 2863
## 111   0  25 120 Other     0   0  0  1   2 2877
## 112   0  28 167 White     0   0  0  0   0 2877
## 113   0  17 122 White     1   0  0  0   0 2906
## 114   0  29 150 White     0   0  0  0   2 2920
## 115   0  26 168 Black     1   0  0  0   0 2920
## 116   0  17 113 Black     0   0  0  0   1 2920
## 117   0  17 113 Black     0   0  0  0   1 2920
## 118   0  24  90 White     1   1  0  0   1 2948
## 119   0  35 121 Black     1   1  0  0   1 2948
## 120   0  25 155 White     0   0  0  0   1 2977
## 121   0  25 125 Black     0   0  0  0   0 2977
## 123   0  29 140 White     1   0  0  0   2 2977
## 124   0  19 138 White     1   0  0  0   2 2977
## 125   0  27 124 White     1   0  0  0   0 2922
## 126   0  31 215 White     1   0  0  0   2 3005
## 127   0  33 109 White     1   0  0  0   1 3033
## 128   0  21 185 Black     1   0  0  0   2 3042
## 129   0  19 189 White     0   0  0  0   2 3062
## 130   0  23 130 Black     0   0  0  0   1 3062
## 131   0  21 160 White     0   0  0  0   0 3062
## 132   0  18  90 White     1   0  0  1   0 3062
## 133   0  18  90 White     1   0  0  1   0 3062
## 134   0  32 132 White     0   0  0  0   4 3080
## 135   0  19 132 Other     0   0  0  0   0 3090
## 136   0  24 115 White     0   0  0  0   2 3090
## 137   0  22  85 Other     1   0  0  0   0 3090
## 138   0  22 120 White     0   0  1  0   1 3100
## 139   0  23 128 Other     0   0  0  0   0 3104
## 140   0  22 130 White     1   0  0  0   0 3132
## 141   0  30  95 White     1   0  0  0   2 3147
## 142   0  19 115 Other     0   0  0  0   0 3175
## 143   0  16 110 Other     0   0  0  0   0 3175
## 144   0  21 110 Other     1   0  0  1   0 3203
## 145   0  30 153 Other     0   0  0  0   0 3203
## 146   0  20 103 Other     0   0  0  0   0 3203
## 147   0  17 119 Other     0   0  0  0   0 3225
## 148   0  17 119 Other     0   0  0  0   0 3225
## 149   0  23 119 Other     0   0  0  0   2 3232
## 150   0  24 110 Other     0   0  0  0   0 3232
## 151   0  28 140 White     0   0  0  0   0 3234
## 154   0  26 133 Other     1   2  0  0   0 3260
## 155   0  20 169 Other     0   1  0  1   1 3274
## 156   0  24 115 Other     0   0  0  0   2 3274
## 159   0  28 250 Other     1   0  0  0   6 3303
## 160   0  20 141 White     0   2  0  1   1 3317
## 161   0  22 158 Black     0   1  0  0   2 3317
## 162   0  22 112 White     1   2  0  0   0 3317
## 163   0  31 150 Other     1   0  0  0   2 3321
## 164   0  23 115 Other     1   0  0  0   1 3331
## 166   0  16 112 Black     0   0  0  0   0 3374
## 167   0  16 135 White     1   0  0  0   0 3374
## 168   0  18 229 Black     0   0  0  0   0 3402
## 169   0  25 140 White     0   0  0  0   1 3416
## 170   0  32 134 White     1   1  0  0   4 3430
## 172   0  20 121 Black     1   0  0  0   0 3444
## 173   0  23 190 White     0   0  0  0   0 3459
## 174   0  22 131 White     0   0  0  0   1 3460
## 175   0  32 170 White     0   0  0  0   0 3473
## 176   0  30 110 Other     0   0  0  0   0 3544
## 177   0  20 127 Other     0   0  0  0   0 3487
## 179   0  23 123 Other     0   0  0  0   0 3544
## 180   0  17 120 Other     1   0  0  0   0 3572
## 181   0  19 105 Other     0   0  0  0   0 3572
## 182   0  23 130 White     0   0  0  0   0 3586
## 183   0  36 175 White     0   0  0  0   0 3600
## 184   0  22 125 White     0   0  0  0   1 3614
## 185   0  24 133 White     0   0  0  0   0 3614
## 186   0  21 134 Other     0   0  0  0   2 3629
## 187   0  19 235 White     1   0  1  0   0 3629
## 188   0  25  95 White     1   3  0  1   0 3637
## 189   0  16 135 White     1   0  0  0   0 3643
## 190   0  29 135 White     0   0  0  0   1 3651
## 191   0  29 154 White     0   0  0  0   1 3651
## 192   0  19 147 White     1   0  0  0   0 3651
## 193   0  19 147 White     1   0  0  0   0 3651
## 195   0  30 137 White     0   0  0  0   1 3699
## 196   0  24 110 White     0   0  0  0   1 3728
## 197   0  19 184 White     1   0  1  0   0 3756
## 199   0  24 110 Other     0   1  0  0   0 3770
## 200   0  23 110 White     0   0  0  0   1 3770
## 201   0  20 120 Other     0   0  0  0   0 3770
## 202   0  25 241 Black     0   0  1  0   0 3790
## 203   0  30 112 White     0   0  0  0   1 3799
## 204   0  22 169 White     0   0  0  0   0 3827
## 205   0  18 120 White     1   0  0  0   2 3856
## 206   0  16 170 Black     0   0  0  0   4 3860
## 207   0  32 186 White     0   0  0  0   2 3860
## 208   0  18 120 Other     0   0  0  0   1 3884
## 209   0  29 130 White     1   0  0  0   2 3884
## 210   0  33 117 White     0   0  0  1   1 3912
## 211   0  20 170 White     1   0  0  0   0 3940
## 212   0  28 134 Other     0   0  0  0   1 3941
## 213   0  14 135 White     0   0  0  0   0 3941
## 214   0  28 130 Other     0   0  0  0   0 3969
## 215   0  25 120 White     0   0  0  0   2 3983
## 216   0  16  95 Other     0   0  0  0   1 3997
## 217   0  20 158 White     0   0  0  0   1 3997
## 218   0  26 160 Other     0   0  0  0   0 4054
## 219   0  21 115 White     0   0  0  0   1 4054
## 220   0  22 129 White     0   0  0  0   0 4111
## 221   0  25 130 White     0   0  0  0   2 4153
## 222   0  31 120 White     0   0  0  0   2 4167
## 223   0  35 170 White     0   1  0  0   1 4174
## 224   0  19 120 White     1   0  0  0   0 4238
## 225   0  24 116 White     0   0  0  0   1 4593
## 226   0  45 123 White     0   0  0  0   1 4990
## 4     1  28 120 Other     1   1  0  1   0  709
## 10    1  29 130 White     0   0  0  1   2 1021
## 11    1  34 187 Black     1   0  1  0   0 1135
## 13    1  25 105 Other     0   1  1  0   0 1330
## 15    1  25  85 Other     0   0  0  1   0 1474
## 16    1  27 150 Other     0   0  0  0   0 1588
## 17    1  23  97 Other     0   0  0  1   1 1588
## 18    1  24 128 Black     0   1  0  0   1 1701
## 19    1  24 132 Other     0   0  1  0   0 1729
## 20    1  21 165 White     1   0  1  0   1 1790
## 22    1  32 105 White     1   0  0  0   0 1818
## 23    1  19  91 White     1   2  0  1   0 1885
## 24    1  25 115 Other     0   0  0  0   0 1893
## 25    1  16 130 Other     0   0  0  0   1 1899
## 26    1  25  92 White     1   0  0  0   0 1928
## 27    1  20 150 White     1   0  0  0   2 1928
## 28    1  21 200 Black     0   0  0  1   2 1928
## 29    1  24 155 White     1   1  0  0   0 1936
## 30    1  21 103 Other     0   0  0  0   0 1970
## 31    1  20 125 Other     0   0  0  1   0 2055
## 32    1  25  89 Other     0   2  0  0   1 2055
## 33    1  19 102 White     0   0  0  0   2 2082
## 34    1  19 112 White     1   0  0  1   0 2084
## 35    1  26 117 White     1   1  0  0   0 2084
## 36    1  24 138 White     0   0  0  0   0 2100
## 37    1  17 130 Other     1   1  0  1   0 2125
## 40    1  20 120 Black     1   0  0  0   3 2126
## 42    1  22 130 White     1   1  0  1   1 2187
## 43    1  27 130 Black     0   0  0  1   0 2187
## 44    1  20  80 Other     1   0  0  1   0 2211
## 45    1  17 110 White     1   0  0  0   0 2225
## 46    1  25 105 Other     0   1  0  0   1 2240
## 47    1  20 109 Other     0   0  0  0   0 2240
## 49    1  18 148 Other     0   0  0  0   0 2282
## 50    1  18 110 Black     1   1  0  0   0 2296
## 51    1  20 121 White     1   1  0  1   0 2296
## 52    1  21 100 Other     0   1  0  0   4 2301
## 54    1  26  96 Other     0   0  0  0   0 2325
## 56    1  31 102 White     1   1  0  0   1 2353
## 57    1  15 110 White     0   0  0  0   0 2353
## 59    1  23 187 Black     1   0  0  0   1 2367
## 60    1  20 122 Black     1   0  0  0   0 2381
## 61    1  24 105 Black     1   0  0  0   0 2381
## 62    1  15 115 Other     0   0  0  1   0 2381
## 63    1  23 120 Other     0   0  0  0   0 2410
## 65    1  30 142 White     1   1  0  0   0 2410
## 67    1  22 130 White     1   0  0  0   1 2410
## 68    1  17 120 White     1   0  0  0   3 2414
## 69    1  23 110 White     1   1  0  0   0 2424
## 71    1  17 120 Black     0   0  0  0   2 2438
## 75    1  26 154 Other     0   1  1  0   1 2442
## 76    1  20 105 Other     0   0  0  0   3 2450
## 77    1  26 190 White     1   0  0  0   0 2466
## 78    1  14 101 Other     1   1  0  0   0 2466
## 79    1  28  95 White     1   0  0  0   2 2466
## 81    1  14 100 Other     0   0  0  0   2 2495
## 82    1  23  94 Other     1   0  0  0   0 2495
## 83    1  17 142 Black     0   0  1  0   0 2495
## 84    1  21 130 White     1   0  1  0   3 2495
aggregate(bwt ~ race, length, data=dat)
##    race bwt
## 1 Black  26
## 2 Other  67
## 3 White  96