R数据帧中的增量ID [英] Incremental IDs in a R data frame

问题描述

我有以下数据框：

> test = data.frame(A = sample(1:5, 10, replace = T)) %>% arrange(A)
> test

   A
1  1
2  1
3  1
4  2
5  2
6  2
7  2
8  4
9  4
10 5

I现在希望每一行都有一个ID只有当A值更改时才会增加。这是我试过的：

I now want every row to have an ID that is only incremented when the value of A changes. This is what I have tried:

> test = test %>% mutate(id = as.numeric(rownames(test))) %>% group_by(A) %>% mutate(id = min(id))
> test

       A    id
   (int) (dbl)
1      1     1
2      1     1
3      1     1
4      2     4
5      2     4
6      2     4
7      2     4
8      4     8
9      4     8
10     5    10

但是，我想得到以下内容：

However, I would like to get the following:

       A    id
   (int) (dbl)
1      1     1
2      1     1
3      1     1
4      2     2
5      2     2
6      2     2
7      2     2
8      4     3
9      4     3
10     5     4

推荐答案

library(dplyr)

test %>% mutate(id = dense_rank(A))

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