如何用数据集中其他地方的等效值替换 NA？

我试图寻找一个类似的问题，但找不到一个。如果你这样做，请告诉我！

我一直在研究谷物主食的项目

这是我的数据集的一个子集：

                nutrient.component.      grain nutrients
1                Beta-carotene (μg) White Rice      0.00
2                Beta-carotene (μg) Brown Rice        NA
3                      Calcium (mg) White Rice     28.00
4                      Calcium (mg) Brown Rice     23.00
5                 Carbohydrates (g) White Rice     80.00
6                 Carbohydrates (g) Brown Rice     77.00
7                       Copper (mg) White Rice      0.22
8                       Copper (mg) Brown Rice        NA
9                       Energy (kJ) White Rice   1528.00
10                      Energy (kJ) Brown Rice   1549.00
11                          Fat (g) White Rice      0.66
12                          Fat (g) Brown Rice      2.92
13                        Fiber (g) White Rice      1.30
14                        Fiber (g) Brown Rice      3.50
15           Folate Total (B9) (μg) White Rice      8.00
16           Folate Total (B9) (μg) Brown Rice     20.00
17                        Iron (mg) White Rice      0.80
18                        Iron (mg) Brown Rice      1.47
19           Lutein+zeaxanthin (μg) White Rice      0.00
20           Lutein+zeaxanthin (μg) Brown Rice        NA
21                   Magnesium (mg) White Rice     25.00
22                   Magnesium (mg) Brown Rice    143.00
23                   Manganese (mg) White Rice      1.09
24                   Manganese (mg) Brown Rice      3.74
25  Monounsaturated fatty acids (g) White Rice      0.21
26  Monounsaturated fatty acids (g) Brown Rice      1.05
27                 Niacin (B3) (mg) White Rice      1.60
28                 Niacin (B3) (mg) Brown Rice      5.09
29       Pantothenic acid (B5) (mg) White Rice      1.01
30       Pantothenic acid (B5) (mg) Brown Rice      1.49
31                  Phosphorus (mg) White Rice    115.00
32                  Phosphorus (mg) Brown Rice    333.00
33  Polyunsaturated fatty acids (g) White Rice      0.18
34  Polyunsaturated fatty acids (g) Brown Rice      1.04
35                   Potassium (mg) White Rice    115.00
36                   Potassium (mg) Brown Rice    223.00
37                      Protein (g) White Rice      7.10
38                      Protein (g) Brown Rice      7.90
39              Riboflavin (B2)(mg) White Rice      0.05
40              Riboflavin (B2)(mg) Brown Rice      0.09
41        Saturated fatty acids (g) White Rice      0.18
42        Saturated fatty acids (g) Brown Rice      0.58
43                    Selenium (μg) White Rice     15.10
44                    Selenium (μg) Brown Rice        NA
45                      Sodium (mg) White Rice      5.00
46                      Sodium (mg) Brown Rice      7.00
47                        Sugar (g) White Rice      0.12
48                        Sugar (g) Brown Rice      0.85
49                 Thiamin (B1)(mg) White Rice      0.07
50                 Thiamin (B1)(mg) Brown Rice      0.40
51                   Vitamin A (IU) White Rice      0.00
52                   Vitamin A (IU) Brown Rice      0.00
53                  Vitamin B6 (mg) White Rice      0.16
54                  Vitamin B6 (mg) Brown Rice      0.51
55                   Vitamin C (mg) White Rice      0.00
56                   Vitamin C (mg) Brown Rice      0.00
57 Vitamin E, alpha-tocopherol (mg) White Rice      0.11
58 Vitamin E, alpha-tocopherol (mg) Brown Rice      0.59
59                  Vitamin K1 (μg) White Rice      0.10
60                  Vitamin K1 (μg) Brown Rice      1.90
61                        Water (g) White Rice     12.00
62                        Water (g) Brown Rice     10.00
63                        Zinc (mg) White Rice      1.09
64                        Zinc (mg) Brown Rice      2.02

糙米有四个 NA 值。
根据这张图，我认为可以公平地假设糙米的 NA 值将非常接近白米的等效值。并且镜像白米值而不是将值转换为零会更准确。

我的问题是，除了手动查找和输入糙米的白米当量营养素外，代码如何将 NA 替换为白米的等效值？我希望结果能转换铜的 NA 值；糙米与铜的价值相同；白米（0.22）。首先用零替换NA会更好吗？但是如果我这样做，那么我就有六种营养价值为零而不是四个数值为 NA 的营养素。我试图找出正确的心态来通过代码解决这个问题。对此的任何见解将不胜感激。

谢谢