各位大神好,
df <- data.frame(index = 1:20, name = c("A", "B", "C", "A", "A", "C", "B", "C", "A", "B", "C", "A", "A", "A", "C", "B", "C", "A", "B", "C"), amount = c(10,14,3,4,15,9,12,6,7,8,10,13,12,6,8,8,9,3,14,10))
| index | name | amount |
1 | A | 10 |
2 | B | 14 |
3 | C | 3 |
4 | A | 4 |
5 | A | 15 |
6 | C | 9 |
7 | B | 12 |
8 | C | 6 |
9 | A | 7 |
10 | B | 8 |
11 | C | 10 |
12 | A | 13 |
13 | A | 12 |
14 | A | 6 |
15 | C | 8 |
16 | B | 8 |
17 | C | 9 |
18 | A | 3 |
19 | B | 14 |
20 | C | 10 |
請問在 R 如何可以做出下面code 的效果呢 ?
| index | name | amount | code |
| 1 | A | 10 | A.10 |
| 2 | B | 14 | B.14 |
| 3 | C | 3 | C.03 |
| 4 | A | 4 | A.04 |
| 5 | A | 15 | A.15 |
| 6 | C | 9 | C.09 |
| 7 | B | 12 | B.12 |
| 8 | C | 6 | C.06 |
| 9 | A | 7 | A.07 |
| 10 | B | 8 | B.08 |
| 11 | C | 10 | C.10 |
| 12 | A | 13 | A.13 |
| 13 | A | 12 | A.12 |
| 14 | A | 6 | A.06 |
| 15 | C | 8 | C.08 |
| 16 | B | 8 | B.08 |
| 17 | C | 9 | C.09 |
| 18 | A | 3 | A.03 |
| 19 | B | 14 | B.14 |
| 20 | C | 10 | C.10 |
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